What problems can be with Dell Flat Screen Monitor?

Why is my screen/monitor not being detected? Detailed?

• My uncle changed the hard drive on my Dell Microsoft XP Version 2002 computer during the summer. he added a couple of graphics sticks and a spare hard drive inside of it. Due to the surpassing of the computers regular resources... i could no longer use the regular blue port for the monitor's cord. I went to best buy to purchase a multiple prong cord converter (11-vb or something like that) for the very bottom of my computer where there are two different white ports. Without it my monitor would not show the contents of the computer. It would come on but the contents of the computer were not showing. After i got the converter i had few problems with the screen. But now i constantly have to abruptly turn my computer on and off and on and off again for the computer to detect the monitor. and i'm worried about it hurting my computer. Is there anyway to solve this problem at all? :(

• Answer:

  You are hurting your computer. He probably taxed out the power supply. Two graphic cards and another hard drive drain more power from the power supply. Try disconnecting the power on the extra hard drive. But first contact your uncle on this.