Why is my computer making a beeping noise and freezing on start up?

When I start my computer it beeps once then it beeps continuously until I shut it off. My monitor works fine. When the computer starts up I get the computer start up screen, then the beeping starts and it freezes. It never gets pass the start up screen. Please help! The computer is a compaq presario, 2.6GHz celeron processor, 512MB ram memory, 80GB hard drive, running windows xp.

check the RAM for loose contact