Computer powers but shorts out monitor

My computer was in storage and when I went to start it up, My system powered up but shorted out the monitor. Also my keyboard does not work as well, I replaced the power supply however, got the same results.
Could it be the Cmos chip from sitting so long, I have checked all of the connections in and out of the case.
Would appreciate a solution
The system is a Gateway Slot p11 400mhz with a 10 gig hard drive and is about 3 years old.
Thanks so much,
Brenda