Computer has begun to lock-up

[Rigsby]

OK where do I start...mmmmm......

Since about a week ago my computer randomly freezes. By that I mean - whether or not I'm actively using it - a window will pop up saying 'insufficient resources to process command' - and eventually anything thats open will become unresponsive. The text will disappear on the taskbar buttons. Ctrl-alt-del will give an error and not display the task manager. I then have to pull-the-plug so to speak.

I use MS Outlook 2003 and that may or may not crash a few times on starting-up but if I persist with it (and keep re-starting it), I can eventually login & it's OK.

I have SP3 totally up-to-date. I've uninstalled & re-installed Online Armor firewall & Avira Anti-virus plus Malawarebytes & SuperAntiSpyware. All run clean indicating no viruses, spyware, etc etc.

I've restored an image of the C-drive from 2 months ago - way before this started happening, but the problem persists. I've also run Windows Memory Diagnostic test & it passes OK. I've unseated/reseated the RAM (physically).

Anyone any ideas on what's going on here ??

Thanks in anticipation.