I just built a computer for my daughter and ran into a problem. I'll start with specs

Mobo: ECS HT2000 GeForce 6100sm-m (onboard video and audio)
Processor: AMD 64 X2 4200+ 2.2ghz Socket AM2
Memory: 1Gb OCZ DDR2 667
HD: Western Digital 80Gig Sata
PSU: 480W El cheapo
Problem: I installed the mobo into tower and plugged everything in, power supply in tower is only a 20 pin but powers up just the same. I'm using the onboard video and sound for now. The motherboard gets power but all I can get is a constant flow of short beeps, there's no use counting they never stop. So I tried clearing the CMOS, still no go. Next I tried another stick of memory (1GB DDR2 800mhz which I know is good) still no go, motherboard just beeps. I thought that maybe the PSU wasn't supplying enough power, so I switched over my OCZ 800W 24 pin still beeps. I looked in the manual and it says that a 20 pin PSU was ok to install.
The only thing I can see is that either my processor is dead (It worked fine in my pc though) or I bought a faulty motherboard (but it gets power because all fans turn, hd comes on and it beeps).
If anybody has a solution, please feel free to share your knowledge.
Thanks in advance