Show your log messages.

A couple of comments (that may be way off the mark ...):

First off, I'm assuming that your CPU cache isn't so full it doesn't need to call for CPU work. Are any work units running already?

Then, are the preferences you're talking about set on the host (the WCG web site), but have you overridden them in the client? Once you set anything in the client, that wins over the host. There's a button in the client dialogue to clear all the changes and return to host settings. If you're running other BOINC projects as well as WCG there are multiple hosts involved and it gets more complicated. I've never done that, but I think I would recommend setting everything on the client in those circumstances (and that's my preference anyway). If using the host settings, make sure you have "Allow research to run on my CPU?" set to Yes, and CPU usage set high enough to use at least one of your CPUs. (Personally I let BOINC use everything it wants to; I find it well behaved.)

Otherwise, I vaguely remember someone else saying something similar and I was wondering if they were using a version of BOINC other than the WCG tested version, and wondered if it was bugged. But I probably got that wrong.

Finally, all I can suggest is that you uninstall and start again with a clear system.