For a couple months now, my computer has been freezing after it has been turned on for about 10 min. When i go too restart it, it has "no signal" on the monitor, but the computer is still on. What could this be?
Sounds like a video card. Sometimes off-board video cards can gather dust along the contacts and cause problems, or it may just need to be re-seated (taken out and put back in) to make the connections work better. Commonly, a cooling fan quits and causes the GPU to over-heat.
I would disconnect the power, open the lid and see if dust may be an issue. Was there any noise from the fan(s) before this issue? To clean out dust, a compressor works best, but make sure you hold any fans still while blasting them with air... Turning them too fast may cause problems. If you don't have access to an air compressor, canned air is ok, but us short bursts and keep the can upright to avoid frost and/or liquid from discharging. A vacuum is my least favorite way to clean a PC since it does not do a very good job and can build up static electricity (which can kill your PC).
After you are free from dust, leave the cover off and power up the system. I shouldn't have to say this, but don't put anything inside the machine when the cord is attached (even if it is "off"). As it powers up, make sure all the fans are turning.