Counter-strike source random crashes

Hi, I'm not sure if this is the correct category to post this in please tell me if it isn't. I just built this system mainly for school classes, but also to play games. having a problem with Counter-strike Source crashing after 15 minutes up to a hour of play. Even sometimes it will crash after loading up the server. Also on occasion the whole system will restart which makes me wonder why this is doing it. I run bootcamp on my macbook pro and can play counter-strike perfectly fine. This is very strange because my new build has very comparable specs to my macbook pro.

Here is what I have put together.

Mobo:ASUS P5QL PRO LGA 775 Intel P43 ATX Intel
PSU: COOLMAX CU-700B 700W ATX 12V V2.2/EPS 12V V2.91 SLI Ready CrossFire Ready Modular Power Supply
CPU:Intel Core 2 Duo E8400 Wolfdale 3.0GHz LGA 775 65W Dual-Core Processor Model BX80570E8400
RAM: OCZ Reaper HPC 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory Model OCZ2RPR10664GK
Graphics: Radeon X1950

I would like to add that I received the Radeon X1950 from my father. Is it possible if it has been overclocked prior to being in my machine to still stay overclocked. Just curious I have never done overclocking before.