Full-screen programs refuse to stay full-screen

This happens with many of my full-screen games, but at times it will occur
with other programs including the screensaver! When I start a program, it
will begin as it should and go to full-screen, but then it will minimize and
return to the desktop. I can see the program listed on the taskbar, and if I
click on it, it will "attempt" to go full-screen, but return immediately to
the desktop. The programs/games that have the problem, always have the
problem. The ones that work fine, always work fine, it seems. But, as it's
not just one or 2 programs, it has to be in the OS or graphics somewhere.

Another odd thing going on that may be related: At one time, I had a
dual-monitor system. Experiencing simalr problems where the programs wouldn't
show on the monitor I assigned them to, I gave up and removed the 2nd
monitor. Now, with only one monitor, I seem to be forced to have my current
monitor assigned as monitor #2.

Anyone with any ideas of the problem and/or a solution??

Here's my system specs:
AMD Athlon 64 3000+
2.0 Gb RAM
ATI Radeon X1650 card (AGP 8X)
Vista 32 Bit OS (4.0 Rating)