Mac Mini stuck in boot loop!

I have a Mac Mini that has a 1.83Hz Core 2 Duo processor with 1 GB of DDR2 SDRAM, and a 80 GB HD. For no apparent reason it is stuck in a boot loop. When I turn the Mac Mini system on it starts on the grey screen and then gives me this error message "You need to restart your computer. Hold down the power button for several seconds or press the restart button." Behind this message are some weird error codes and this message "Mac OS Version: Not Yet Set"

I'm also unable to boot from CD using the C command on startup, it just gives me the same restart message. The only thing I can get into from the boot commands is the Hardware testing, and I've received this error message "4MEM/4/40000000x3b8bo390"

This problem has happened to me before so I just left my mac mini alone for almost a year. 2 days ago I decided to boot it up and it actually let me boot from the CD. So I erased the HD and reinstalled the OS. Well it was working fine for 2 days and then the exact same thing is happening again. What can I do? HELP!!!!