PLEASE HELP! No signal to Monitor, Keyboard, and Mouse but PC and fan turns on!

I had this happen to me once. I fixed it, can't remember exactly how though...big help right?

Google is your friend, I know the answer is out there so don't panic much.

Here are the troubleshooting steps to go through. This is a lengthy process, but through. It is a good chance it is the power supply but we are testing for bad components as well.

Step 1:
Start by removing everything, even fans. Your CPU isn't very active at this point so you'll have some time. Also, unplug the PSU from the wall and wait about 30min to an hour. PSUs still hold power for a little bit. (I just did this for a mobo that wouldn't turn on, after which, it did.)
Step 2:
Unplug all power connectors from the motherboard and wait a few minutes. Capacitors still hold a charge.
(For both step 1 and 2, hitting the power button might help this go faster.) Remove the CMOS battery and use the BIOS reset it using the jumper on the mobo. If you dont have one, you can use a paper clip to bridge the battery connectors together for a few moments.
Step 3:
Make sure everything is unplugged from the mobo including connectors to the reset switch, HDD LED, Power LED, etc. Absolutely everything should be disconnected. All cards including RAM should be removed, all drive cables should be removed.
Use compressed air to blow off any potential dust on the mobo including slots. If using an air can, besure to keep it upright and level.
If you can, take the mobo and PSU out of the case and sit it down on a table or wood (NOT CARPET)
Through these steps, use the power button on your mobo if you have one or use a paper clip and tap the two power pins together.
You're looking for 'good' beeps, usually a single beep signaling everything is fine. Long beeps or beeping in a pattern are 'bad' beeps. These are actually good once the basic components are on the mobo (CPU, RAM, power connectors.)
- Plug in the main 24-pin power cable. If you have a CPU power connector, don't plug it in yet. No video card yet.
- Touch the power switch pins. If there is no beeping, it could be the power supply but we have not eliminated the mobo or PSU yet.
- You are going to connect one thing at a time and try powering up every time you do.. I would go in this order...
CPU power connector
One RAM stick tried in each slot, if you have another stick of RAM, then leave them in.
*It might be worth reseating the CPU as well but only if you have thermal paste on hand. I would consider doing this at the very end too. You'll want to clean up any excess thermal paste if you find any. You will only ever want to use half a pea size ball in the middle of the CPU.
Fans, one at a time, CPU first but plug a different fan to the CPU fan connector first. If that works, try the actual CPU fan.
After testing these, leave just the CPU fan plugged in.
Video card but don't connect monitor
If you have more than one PCIe slot that can take a video card, try them.
If your video card uses a power plug, don't use it yet.
Connect the video card power, if applicable. If your PSU has more than one video card power cable, use one that you weren't
Last, connect monitor. Try different video ports if possible. You could also do this at the very end. We're mostly looking for beeps, not video output.
Start with drives, HDD/SSD first
Use different power cables, not just plugs
Use different SATA cables, if you don't have spares, switch then around
Use different SATA ports

Again, during this process, we want 'good' beeps more than anything. Single beeps are good but multiple beeps or no beeps are all are bad. If you get to the point of having just the CPU, RAM and main and cpu power cables connected and have 'good' beeping, I'd say the mobo is fine but the PSU could still be an issue. You need to get to having the CPU, RAM, fan and main power and CPU power plugs before calling it. I would say, get another PSU at this point.

If you get a new PSU, ALWAYS BUY NEW!. Start with Best Buy. Their prices are not that bad compared to online retailers. If it doesn't fix the problem, you can usually take it back without issue. Don't get their Dynex brand. Go with Corsair first, then Thermaltake next. You'll find Antec PSUs at Staples which I would put above Thermaltake, however, I had a Thermaltake PSU last well past warranty until I recycled it. Staples does charge more usually than online retailers but the possibility to return it makes it a viable option. Make sure to get one with enough wattage.

If you think that any of the components went bad, I would still consider the PSU as the culprit. I recently had to replace my PSU because it started to slowly not handle the power draw. I found that out that if I lowered my videocard clock speed for modern games, the system would not crash. Older, less demanding games would work fine. This got worse over a few weeks. There were no problems after replacing the PSU.

Good luck!

(Sorry if this seems rough, I don't have much time right now to clean it up)

P.S. A hair dryer won't give you enough force. Air cans are the way to go. You can get thoes practically anywhere including walmart.