To start, I am a complete noob at computers so Im not quite sure what Im doing. Recently while playing games my computer screen faded to black, followed a few seconds later with my entire computer dying. I tried everything to turn it back on but had no luck whatsoever. I decided that the best course of action would be to get a new power supply, so I went out and replaced the old 600 watt power supply with a 550 Thremaltake gaming power supply. I installed the psu with no problems and when i turned on the computer everything seemed to run ok, but there is no signal on the monitor. The monitor power supply is ok, i checked it and there is a yellow light and it says there is no signal. I made sure to plug in the special pci exspress connector to the video card and so I am very sure that everything has power, so I dont know what the problem could be, but heres what I was thinking.

1. Because I got a 550 psu insted of 600, there is not enough power BUT the computer is atleast 3 years old and the video card is not brand new, so I was thinking that would be ok.

2. Something happened to the monitor when the computer died as well and I should just get a new monitor.

3. Something happened to the video card when the psu died and so now I need to replace that.

Because this computer was built by someone else a few years ago I am not quite sure what the monitor or graphics card is, currently there is 2 hard drives, a motherboard, dvd drive, graphics card, and a thermaltake water cooling device attached to the PSU, does anybody have any suggestions of what I should do.