Please help -reboot infinite loop

hello

I have an inspition 8100 that I bought used last year and have nothing but trouble ever since, I am tired of taking it back to the store where I bought it to have it fixed and I am hoping someone can tell me what the heck is going on and how to fix it myself instead of paying $100 and loosing my computer for several days...

here is the problem and it has happened several times before..

 

When I start my computer it will go to the dell screen, then the windows screen and it will start to load my desktop. Sometimes it loads it completely but most of time time it doesnt not, then it flashes a blue error screen so fast I cant read the error on it, and then it reboots and trys to start all over again, in a loop over and over again.. This has happened to me so many times that I am sick of it. I am pure and simple not going to take it back to be fixed again! So I am hoping someone might know what is going and and tell me how to do this myself..... I can start in safe mode, with networking.. I am actually on the laptop now in safe mode. I have a disc that the repairman gave me to repair windows when this happens, but it asks for the administrator password which I have no idea of..... think that must be what the repairman did to ensure I kept bringing it back.....

I have:

inspirion 8100

windows xp service pack 2

norton system works 2004 ( virus protection)

If you need anyother info to help me just ask I am desperate to fix this, I have tons of work to do and some of it just cant be done is safe mode, its a real PITA....

Thanks, in advance, for you help

KJ