I have a friend who just built a computer whose specs are as follows:
AMD Phenom II 980 X4
XFX Radeon HD 6870
RipJaws 1600 MHZ 4x2 GB
OCZ 500W PSU
He successfully installed Windows 7 and Battlefield 3 but turned off the computer for the night and now it will not boot up. It will turn on with fans/lights but there is no display. Also, holding the power button will not turn off the system you have to turn the switch on the PSU off to turn it off (the switch will turn the PC on). There are no beeps when turning the PC on and we tried resetting the CMOS.
If the mobo has onboad video try that.
Could be an issue with the video card...another to swap for it?