HP 6735b wont boot, black screen?

I have a HP 6735b that wont boot, the num and caps lock keys flash five times which means a motherboard or other failure. But the other day when it was hit on the keyboard a few times it booted. I completely disembled it to nothing and checked every part including the motherboard for visual faults but found nothing, this all started after it was on stand by and frozen one day. When it booted the other day i also flashed the bios with the latest 2010 version. It ran out of warranty a month ago as well. ive left it on trying to boot all day today and it just booted then but once i turn it off it will do the same, i didnt even touch it when it booted just then. Any ideas?