I am getting no usable GPUs found. I will try to give enough info to help. I've been crunching for 16 years and this is one of the first problems I have had.

Event log lines:
4/10/2015 4:58:08 PM | | cc_config.xml not found - using defaults
4/10/2015 4:58:08 PM | | Starting BOINC client version 7.4.42 for windows_x86_64
4/10/2015 4:58:08 PM | | log flags: file_xfer, sched_ops, task
4/10/2015 4:58:08 PM | | Libraries: libcurl/7.39.0 OpenSSL/1.0.1j zlib/1.2.8
4/10/2015 4:58:08 PM | | Running as a daemon
4/10/2015 4:58:08 PM | | Data directory: C:\ProgramData\BOINC
4/10/2015 4:58:08 PM | | Running under account boinc_master
4/10/2015 4:58:08 PM | | No usable GPUs found
4/10/2015 4:58:08 PM | | Host name: Octocore
4/10/2015 4:58:08 PM | | Processor: 8 AuthenticAMD AMD FX(tm)-8350 Eight-Core Processor [Family 21 Model 2 Stepping 0]
4/10/2015 4:58:08 PM | | Processor features: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 htt pni ssse3 fma cx16 sse4_1 sse4_2 popcnt aes f16c syscall nx lm avx svm sse4a osvw ibs xop skinit wdt lwp fma4 tce tbm topx page1gb rdtscp bmi1
4/10/2015 4:58:08 PM | | OS: Microsoft Windows 8.1: Core x64 Edition, (06.03.9600.00)
4/10/2015 4:58:08 PM | | Memory: 31.90 GB physical, 63.90 GB virtual
4/10/2015 4:58:08 PM | | Disk: 476.42 GB total, 348.97 GB free
4/10/2015 4:58:08 PM | | Local time is UTC -4 hours
4/10/2015 4:58:08 PM | | VirtualBox version: 4.3.12
4/10/2015 4:58:08 PM | SETI@home | URL http://setiathome.berkeley.edu/; Computer ID 7527083; resource share 100
4/10/2015 4:58:08 PM | PrimeGrid | URL http://www.primegrid.com/; Computer ID 488146; resource share 100
4/10/2015 4:58:08 PM | SETI@home | General prefs: from SETI@home (last modified 07-Mar-2011 09:47:03)
4/10/2015 4:58:08 PM | SETI@home | Computer location: home
4/10/2015 4:58:08 PM | SETI@home | General prefs: no separate prefs for home; using your defaults
4/10/2015 4:58:08 PM | | Reading preferences override file
4/10/2015 4:58:08 PM | | Preferences:
4/10/2015 4:58:08 PM | | max memory usage when active: 16333.75MB
4/10/2015 4:58:08 PM | | max memory usage when idle: 29400.75MB
4/10/2015 4:58:08 PM | | max disk usage: 100.00GB
4/10/2015 4:58:08 PM | | don't compute while active
4/10/2015 4:58:08 PM | | don't use GPU while active
4/10/2015 4:58:08 PM | | suspend work if non-BOINC CPU load exceeds 25%
4/10/2015 4:58:08 PM | | (to change preferences, visit a project web site or select Preferences in the Manager)
4/10/2015 4:58:08 PM | | Not using a proxy

AMD Catalyst Version: 14.12 AMD Catalyst Omega Software
CLINFO output:

C:\clinfo>clinfo
Number of platforms: 1
Platform Profile: FULL_PROFILE
Platform Version: OpenCL 2.0 AMD-APP (1642.5)
Platform Name: AMD Accelerated Parallel Proces
sing
Platform Vendor: Advanced Micro Devices, Inc.
Platform Extensions: cl_khr_icd cl_khr_d3d10_sharing
cl_khr_d3d11_sharing cl_khr_dx9_media_sharing cl_amd_event_callback cl_amd_offl
ine_devices


Platform Name: AMD Accelerated Parallel Proces
sing
Number of devices: 2
Device Type: CL_DEVICE_TYPE_GPU
Device ID: 4098
Max compute units: 20
Max work items dimensions: 3
Max work items[0]: 256
Max work items[1]: 256
Max work items[2]: 256
Max work group size: 256
Preferred vector width char: 4
Preferred vector width short: 2
Preferred vector width int: 1
Preferred vector width long: 1
Preferred vector width float: 1
Preferred vector width double: 1
Max clock frequency: 955Mhz
Address bits: 32
Max memory allocation: 1408499712
Image support: Yes
Max number of images read arguments: 128
Max number of images write arguments: 8
Max image 2D width: 16384
Max image 2D height: 16384
Max image 3D width: 2048
Max image 3D height: 2048
Max image 3D depth: 2048
Max samplers within kernel: 16
Max size of kernel argument: 1024
Alignment (bits) of base address: 2048
Minimum alignment (bytes) for any datatype: 128
Single precision floating point capability
Denorms: No
Quiet NaNs: Yes
Round to nearest even: Yes
Round to zero: Yes
Round to +ve and infinity: Yes
IEEE754-2008 fused multiply-add: Yes
Cache type: Read/Write
Cache line size: 64
Cache size: 16384
Global memory size: 2147483648
Constant buffer size: 65536
Max number of constant args: 8
Local memory type: Scratchpad
Local memory size: 32768
Error correction support: 0
Profiling timer resolution: 1
Device endianess: Little
Available: Yes
Compiler available: Yes
Execution capabilities:
Execute OpenCL kernels: Yes
Execute native function: No
Queue properties:
Out-of-Order: No
Profiling : Yes
Platform ID: 5F6015B0
Name: Pitcairn
Vendor: Advanced Micro Devices, Inc.
Driver version: 1642.5 (VM)
Profile: FULL_PROFILE
Version: OpenCL 1.2 AMD-APP (1642.5)
Extensions: cl_khr_fp64 cl_amd_fp64 cl_khr_
global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int3
2_base_atomics cl_khr_local_int32_extended_atomics cl_khr_int64_base_atomics cl_
khr_int64_extended_atomics cl_khr_3d_image_writes cl_khr_byte_addressable_store
cl_khr_gl_sharing cl_ext_atomic_counters_32 cl_amd_device_attribute_query cl_amd
_vec3 cl_amd_printf cl_amd_media_ops cl_amd_media_ops2 cl_amd_popcnt cl_khr_d3d1
0_sharing cl_khr_d3d11_sharing cl_khr_dx9_media_sharing cl_khr_image2d_from_buff
er cl_khr_spir cl_khr_gl_event

I use a real monitor (39" Seiki running at 3840x2160)
I have done about everything I can think of: Different drivers, different Boinc versions, AMP drivers.

How do I crack this problem of Boinc not detecting the GPU?

I am getting no usable GPUs found. I will try to give enough info to help. I've been crunching for 16 years and this is one of the first problems I have had.

Event log lines:
4/10/2015 4:58:08 PM | | cc_config.xml not found - using defaults
4/10/2015 4:58:08 PM | | Starting BOINC client version 7.4.42 for windows_x86_64
4/10/2015 4:58:08 PM | | log flags: file_xfer, sched_ops, task
4/10/2015 4:58:08 PM | | Libraries: libcurl/7.39.0 OpenSSL/1.0.1j zlib/1.2.8
4/10/2015 4:58:08 PM | | Running as a daemon

The usual, I'm afraid. That line says you made a service install: uninstall BOINC (you won't lose any data), and re-install it using the same folder locations - but visiting the 'Advanced' page on the way through, to uncheck the service install option.

Ahh the simple things you overlook...

uninstall, reinstall, disable service, and appears to be working now.

Thank you for the speedy reply.