SP 2 Download Problems

I have an HP XL-916 I downloaded SP2, and when I get to the windows splash, after restarting, the screen just goes blank. I went into safe mode, and when I tried to uninstall the upgrade, access was denied. How can I get into the system to uninstall?
I tried the “last know config. that worked”, and the same thing happened. I also went to microsoft, they suggested that I go into MS DOS, which I did, by running my boot disks, system still not responding. I cannot even get a command prompt to work. Need some help here, system is vital to our network. Thanks.