HDD LED continusously lit and black screen

I have an old computer laying around and I've been neglecting it due to a dead hard drive.

HP Pavillion a610n
Athlon XP 3000 2.1 GHZ
300 Watt power supply
2 GB DDR PC-2700

Recently replaced the hard drive and put 2 gb ram in. Put everything back together and started it up. I was greeted by a long beep which reoccurred every 5 seconds or so and a black screen.

I strip the whole machine down to nothing and then it turned on but I get no video at all. So I reset the bios and put the video card back in and still a blank screen.

I'm totally lost