Dell poweredge 2500 startup problem

I am not an IT professional but am trying to get a small private school set up with a network.
I have a Dell poweredge 2500 which I set up with server 2003, 2 drives mirrored (operating system etc) and the rest striped.
When I originally started working with the server it wouldn’t boot, I scraped the old thermal compound (it had been sitting for several years and was dry) and put new compound on before setting up server 2003, it worked great for awhile, but is once again not booting. It has the same problem it did. It starts the boot process and gets to the line and then everything locks up. Please give me some advice on what to try to get this up and running.
Thanks,
Bob