HP Pavillion a708n No Screen on startup

PC Specs:
Intel Celeron 330 2.66 GHz, 533 MHz Front side bus, Socket mPGA478
Chipset 845GV
MSI MS-6577 V.4
512 MB PC2700 184 pin, DDR SDRAM

Have been running this Pavilion just fine until last week when I hooked up a projector to the on board vga. It worked fine the first few times, but then once, when I unplugged the projector cable, suddenly the PC froze. And now when I try to boot, the system powers on (meaning the LEDs are lit, the optical drives & the fans are working too) but, there's no display in the monitor.. no beeps. So basically the system isn't booting..

I tried adding a new vga card, a new power supply and even RAM but none of them seem to be the problem.. so what do u think might be wrong? is it possible the motherboard is fried? or could it be the processor?

Thank you in advance for any helpful responses..