What can i do to fix my P.C?

My settings seemed perfect yesterday, but I've been messing around getting my Xbox to work on my monitor, so I have messed with all the settings to best fit my Xbox. But now I have gone back onto my PC and it's all wrong. I have changed all the settings...

The PC boots fine and works great until the monitor just goes out and then I have to kill the power to get the PC back up and running when it does this. I have changed the powersupply, RAM, hard drive and even the video card.

I have connected my monitor to another PC and it works perfectly i am guessing it is the PC. Is their any keys I can push to restart it. I am using windows xp. please help.

what program is free, safe to use, downloadable, and wont damage my laptop in any type of way? but as in program i mean as in like norton and mcAfee. i have mcafee but i didnt buy it, all it does is scan my laptop. but it doesnt fix it and my laptop...

My pc wont install vent or anyother program says the file is corrupted, i try to do the same on my other pcs n they work what can i do to fix this? Its a Gateway Vista 64 bit

my pc get stuck often and just runs crappy, i got a message that it was low on memory so how can i get more memory or fix the problem?

I bought this PC 4 days ago and now it's doing this: http://www.youtube.com/watch?v=OQPKxOEXRSU My PC's Specs are: Windows 7 Ultimate 32Bit AMD Athlon II X2 250 Processor 3.0GHz 4Gb Ram ATI Radeon HD 5400 1GB

this only happens when i play pc games, and when im on skype with friends i am playing with. it gets annoying and ruins the purpose when your playing late at night. if anyone has had this problem please let me know stat. thanks.

My computer keeps abruptly shutting off (at least once every hour). The monitor goes to sleep during this time. When it does shut off, it starts trying to power back on after only a few seconds. It doesn't take right away though - like it will go on...