My brand new comp keeps crashing!

I just build a new computer and sometimes *more and more frequently* I get the dreaded blue screen of death. The comp reboots and POST runs w/o error and in a while it might happen again. Its only happened while using graphic intensive applications like video games and the internet so I thought maybe it could be the graphics card. What should I do?

heres the specs...
Biostar TForce6100-939 MOBO
VGA BFG 7900GT O.C. (never had stock overclock could this be prob?)
AMD X2 dual core 4400+
2 GB ADATA D400 system mem
HD 160GB samsung SATA2
Zonet modem 56K
creative audiology SC