Linux screen

I just installed Linux on one of the systems at school so that I can begin
learning how to use it (Mandrake 7.1). After I logon and then I issue the
command “startx” and the KDE desktop comes up, the monitor begins blinking
off and on intermittently. It seems most often to blank when I move the
mouse. I replaced the PS2 mouse with a serial mouse, and nothing changed.
The monitor and video card are both fine, and the problem goes away when I
logout.

I know almost nothing about this OS, so I don’t have a clue what to look for
or try. Any possible suggestions would be GREATLY appreciated 🙂