Well, I eventually worked out that copying BOINC.scr file (which Windows inconveniently deleted during the last update) into C:\Windows manually now at least allows me to set the screensaver to BOINC, via the Settings/Personalization/Lock Screen/Screen Saver Settings(link at bottom middle) route. It remains to be seen if this works II'll get back to you).

Another (more perplexing) problem is that the setting in BOINC Manager's "Computing Preferences" called "Suspend when computer is in use" does not now seem to work! I have it checked, and while I am merrily
typing this message (or doing anything else on the computer) BIONC activities are all churning away slowing my computer down (all the activities are running full pelt, when in the previous version they used to report "suspended due to use activity" (or words to that effect). They would only re-start running when I stopped typing for about 5 seconds.

Should I revert to the previous version (I am starting to think).....

---

Check that Activity (BOINC Manager->View->Advanced view->Activity menu) is set to "Run based on preferences". If it's set to Run Always, it'll do exactly that.
Also check that boinctray.exe is running. This is the BOINC idle detection program.

---

I updated to 7.10.2 on my Win7 machine where I separate CPU tasks on one client instance and GPU work on a 2nd client instance. Only the 1st instance recognized there was a GPU present. The others said no usable GPUs found.

I was on 7.6 but installed 7.8 over 7.10 and now the other client immediately started running GPU tasks with 7.8.