Monitor Goes Blank After startup

I am using Windows 98. When I start my desktop, it goes through the normal boot up process. When it gets to my desktop, the desktop shows up on the screen for a few seconds, but then it clicks and the screen goes black.

I have hooked up my laptop to the monitor and it works fine.

A couple of times, I have gone into the settings to check and see that all the settings were ok (even though I had no idea what I was looking at). On 2 occasions, the monitor did not go blank, but instead indicated that it had found a virus and showed the following:

e:setup/exe
error in win32/cih
Always enable access?

I tried running my AVG virus scan and it found no viruses.

I am computer-tech-challenged, but this site has helped me with other minor computer questions.

Any ideas?