I found the problem, I have 2 differerent types of RAM installed in my PC, 2x 2GB DDR2 Kingston 800Mhz, and 2x 1GB DDR2 Kingmax 667 Mhz, the Kingmax RAM was not compatabile with Windows 7 so I removed it and all is working fine now. If anyone still gets a blue screen after removing incompatabile RAM then check for other devices such as modems.