Monitor on a new system gets very dim, but doesn't turn off.

[LuckyDog]

The crt monitor on a new P4 1.8 system worked fine for a few hours, but now is barely bright enough to see. The monitor is an open box item, but it works fine on a different computer. The computer that is having problems has a Gainward GeForce3 and is running Windows 2000. THe computer that works with the monitor has a Leadtek GeForce2 Ultra and is running Windows ME. Any ideas on a fix?