I am unable to play games on my custom built pc help?

[Cainpole]

Okay first i'm going to tell you guys what is wrong then i will list specs, i have a gaming problem i play world of warcraft have been for years on this same pc this pc has had MANY MANY bad viruses like wiped out whole thing viruses, so getting past that, I play minecraft and sims, i try to play minecraft on low render distance set on low and everything and it over heats my video card is what i am thinking it does the same with sims 3 too!..Is what happends is after 5-10 min of game play it just shuts off my monitor and says entering power save mdoe and the only thing is to get it out is to hold down the power button on my system and shut it off, i have a case that has blue leds and has a temp and fan control, my fan is always on 85-90 and temp it always around 80-90 F and 20-30 C is what these two blue gauges say on the case, my dad built this pc so here are some specs.
5.2 WEI Lowest being processor at 5.2 and highest being graphics at 5.9
hard disk space- Free Space: 77.01 GB
Description : Realtek RTL8187 Wireless 802.11b/g 54Mbps USB 2.0 Network06 - Motherboard
Model: P5B-Deluxe
Manufacturer: ASUSTeK Computer INC.
3006 ram ( about 2.98 gigs with 16 gigs added virtual memory)
Video card is radeon x1950 pro with 512mg video ram it was a 275$ video card when i bought it back 4 years ago not its not much but it is a pretty good video card i think.
Caption : Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz x2 ~2394MHz
Current Clock Speed: 2394MHz
with windows vista ultimate sorry for long question but i really need help guys thanks!!

 

[Abarbarian]

Take one side of the pc case and if it looks dusty, especially the GFX card fan then follow this guide.

http://www.wikihow.com/Clean-the-Inside-of-a-Computer

https://www.pcreview.co.uk/forums/essential-pc-software-updated-10th-february-2012-a-t2697599.html

Have alook in the above section to find some useful utilitys for monitoring your pc to see what is happening.