Hi Guys,
Thanks for all your suggestions! As you can imagine, the computer crashed yet again so only now could I get replies to any you.
ETAF: once the computer crashes, I can't get past BIOS to even attempt safe mode (at least thus far). But I will try the clean boot option.
I don't have any recovery discs ... bought this one brand new but Vista was already installed on it.
I hope I'm not making anything worse with what seems like my 1,000 attempts to re-boot all the time.
Elvandil - THANK YOU for explaining the RAM situation (it's nice you took the time to let me know that!)
The dust idea makes sense, thank you!

I have my computer on stand where it rests on a "zig zag" plastic base. It's not supposed to block ventilation but maybe it is. I wonder why I haven't had problems for the first year though. I'll try cleaning it out.
Hope you guys will be around - you gave me lots of good ideas. I'll report back with results until this thin works out (hopefully soon).
THANK YOU ALL !!!