Why does my computer monitor keep saying "no signal"?

Computer boots up fine, monitor shows no display.?

• Ok, so my computer has been working fine for awhile now, but the other day I noticed that it was starting to get really slow changing web pages and opening programs and what not. I reset my router, which seemed to help my slow internet, but shortly thereafter it started going slow again. I reset my router again, but it just did the same thing. So, suspecting a virus, I tried system restore a few times, trying different dates, but it always came back after restarting saying "System Restore Incomplete. Try running system restore again.". So, I did, multiple times...but I kept getting the same thing. I tried to use system restore in safe mode but a window would always pop up that says "System Restore cannot protect your computer right now. Please restart and try again.". Getting frustrated I tried System Restore one more time out of safe mode. When it restarted it came to my desktop but nothing popped up, no icons, no start button, no window that says system restore had failed. Just my desktop background. Frustrated as I was, I restarted my computer manually, only to find that my monitor screen was blank, with the green light flashing and no display, period. My num-lock light on my keyboard would not come on, and my red laser mouse's red laser isn't showing up either. I have encountered this problem before, but a few reboots helped shake it out of that state. Alas, after about 3-4 hours messing with it, dusting it out, checking wires, cards, checking anything that could be loose...I noticed everything was the way it was before this technical difficulty. I have tried just about everything I could think of besides taking it to a repair shop, because I have enough experience with computers, I should be able to figure it out myself. Sadly, this is not the case, I seriously have no idea what could be wrong with it. I've tried taking out my graphics card and plugging the VGA cord into the video card that was connected to the motherboard, still get the same issue. Now, this computer is quite old...maybe 5-6 years, it has been repaired multiple times, and has had many upgrades installed. I don't think it is a motherboard issue, because then nothing would come on, right? I messed with my RAM, decreasing and increasing it, but that did nothing. I am seriously at my wits end, and cannot figure out what the hell is up with it. If anyone can help me, I would appreciate it, and remember I cannot get to my desktop at all, so please keep that in mind. I will reply to anyone that tries to help, so thanks in advance. P.s. No beeps, tried a different monitor and got the same thing. Worked fine until trying to use system restore.

• Answer:

  You definitely have a hardware problem. Yank or disconnect everything but the mobo and power supply and see if you get post beeps. If no, the mobo or power supply is bad. If yes, proceed to put pieces back in one by one rebooting each time until you find the problem. EDIT: That is what I mean! EDIT: You're only getting a single beep? Send me an email through my answers profile.