Problems with Fake Virus

Okay somehow this Total XP Security thing was installed we never really installed the program. We were looking how to remove it and we couldn't so we installed Ad-Aware it said to Re-boot the computer, we did and it wouldn't start up past like the boot menu or whatever. Now I tried rebooting it and it wouldn't even go to the boot menu! It's a really old computer but I don't think that's the issue any suggestions??