When I put off the switch of monitor, it is black & CPU running. But when I just on it, CPU starts to reboot?

Answer 1

There is a problem in ur UPS and CMOS setting....fix ur UPS to fix ur problem.

Answer 2

You've got an old and weakened SMPS or UPS. When you switch on a monitor it suddenly draws a lot of currant (about 2000 volts) for a second, then goes normal (that current is needed to charge the CRT screen). Most UPS's are capable to deliver this, but seems like your's is not coping with the load anymore. You may try to disconnect some optional devices from the UPS, and then try, it might supply enough power.