Whenever i try to run a complex program or game on my COMPUTER it will freeze then the screen goes black and then it shuts down. When i restart my computer it SAYS that: WARNING! THE CPU HAS BEEN CHANGED. I have no idea why it says this or what has happened

My system information:
Microsoft Windows XP
Professional
Version 2002
Service Pack 3

Computer
Intel(R)
Pentium(R) D CPU 3.40GHz
3.40GHz, 2.00 GB of ram

The File system is NTFS
My hard drive model is ST3250820AS
With 127 GB of ram

My sound card is NVIDIA High Definition Audio
My video card is NVIDIA GEFORCE 8400GS

I currently do not use a anti virus program because i tend to try to remove them manually myself because i don't trust anti viruses too much.

If someone could please help me id be very thankful!

P.S i am not sure this is in the right thread because i have no idea whats causing this problem or what type of problem it is considered
Sounds like a dead/flat CMOS battery to me...
Part # CR2032...available anywhere.
"Bout the size of a dime on the MBoard...remove all power sources when replacing it.Thank you so much i went around and found another CMOS battery put it in and it works like new thank you!Anytime...
Glad it was a simple solution...we love those here.i know right.
It might have also been over heating because when i replaced the battery i noticed it was dusty so i cleaned it out and i saw that the cp fan was litterly caked with dustIt's good to remember to do that regularly...
I do mine APPROX every 3 months...