Win 2000 reboot failures

I installed the trial version of McAfee antivirus on my computer. When I unistalled it my problem started. My computer will no longer do automatic reboots. If it comes up from a cold shutdown it will go into windows just fine. If I manually resetit or an installed program attempts to reboot it, a black screen comes up and everything halts. The only way to get back into windows is to power it down with the switch on the back and then turn it back on. It will then boot into windows normally. Any idea what the problem is??