HP Pavilion a6110n Desktop PC motherboard instructions

Have you tested the power supply on another system? If you have, then I would shop for another motherboard. A non hp board may require a new windows coa, since the first windows installation is tied to an hp bios. Your board is the M2N68-LA made by asus. It has few if any cpu upgrades. I suggest an asrock N68-CS UCC for $44.99 plus shipping at newegg. It has 2 ddr2 and 2 ddr3 slots, giving you some upgrade options at a great price, if you only need two ram slots. DDR3 only works when you change to an am3 cpu. Otherwise, look at any micro atx motherboard with ddr2 support. Also be prepared to change the power supply. I suggest a 400-500 watt in one of the following brands: antec, corsair, seasonic, or enermax. Cheaper brands tend to fail under load.

clear cmos (remove+reinsert battery)
reseat ram
reseat video (if you have a video card)
if you have onboard video use it on its own (no video card) to test the system

Probably the onboard video has gone, have you tried putting in a video card in the PCI-Ex16 slot, even a cheapo card would be better than the integrated nvidia.