Things I've tried :
Validating cache files ( Steam says it's validated and no files are corrupt )
Clean boot ( removing all non-microsoft startup entries on windows )
Delete and full re-install ( problem persists )
System specs :
OS : Windows 7 X64 Ultimate
Motherboard : ASUS M5A78L
Processor: AMD Vishera FX 8350 8 Core @4Ghz
GPU: Sapphire HD 7950 OC Edition 3GB
Memory: Corsair Vengeance LP 16GB @ 1600mhz
Case: Coolermaster HAF-X