Monitor and Devices turning off suddenly

Does the monitor and devices start up again when you move the mouse?

If yes, it's a power saving mode that's turning the off.

If you look around in Control Panel you can find the Power Options.
Choosing a High Performance power plan should stop the shutting down.

If it's not the power options then it could be a lot of things...
Can you give some more details:
When does this happens and what you are doing when this happens? (is it after 8 hours of gaming, or 10 minutes of youtube, or after you leave the computer idle for 5 hours, etc)
When did the problem start occurring? (since you got the computer a year ago, or last week after you lost power, or after a software or driver update, etc)

Any other helpful information or observations?

It's not the power options. All my devices turn off including my monitor and I can't turn them back on. I try taking them out and plugging them back in but nothing works. I eventually get sick of it and have to restart my computer. I've also noticed after this happens I can't restart my computer right away. I have to wait at least 10 minutes or so which makes me think it's overheating but I'm not sure how to fix it. I guess I could take off the plate and have a fan blow into it.

Ok, does the monitor actually power down (turn off)?
Or does the screen just go blank with the 'no signal message'?

Which ATI Radeon HD video card are you using?
Or is it the motherboard integrated ATI Radeon 4200 video?

It says, "Entering Sleep Mode." Which of course that means there's no signal going to it.

Yeah, it's an ATI Radeon HD 4200. And I'm pretty sure it's integrated into the motherboard.

Right, HD 4200 is the motherboard IGP.
I'm getting a strong impression it's a motherboard problem.
Helps explain the 'other devices' problem as well. They're all attached to the motherboard, right?

Yeah, but the thing is that it manages to work for a while. I got it to work perfectly for like two, three days but now it won't even boot. The monitor and devices just won't turn on. But watch in another couple of days it'll start working perfectly again. It's like it chooses when it wants to work.

I would agree WR2, it's probably the motherboard.

Failing components don't always just grind to halt and stay broken. From your description I wouldn't suspect overheating (otherwise it would fail and recover more predictably).

My advice is to consider a new PC, simply because the issue may be hard to isolate to one component and so may lead to you spending more than the PC is worth if the motherboard doesn't fix it. If you want to fix this one I'd start with the motherboard, however it really could be your PSU or possibly even the CPU.

You can do some testing with a multimeter to check the voltage levels from your PSU, and try running Prime95 and Memtest86 to check your CPU and memory.

I really hope it's not the motherboard. Cuz I really don't have the money to buy a new computer. This one costed $800 dollars and it's been doing this off and on since I got it last year. Will HP fix it for me? If so, how much do they usually charge?

Agreed about it being the possibility of a motherboard issue. It sounds like the motherboard and attached components are having trouble communicating.

The PC should have come with a warranty, I don't know how much of one though. Frankly, they should fix it for free, getting them to stand behind their product could be a little tough though.

edit: If they give you any guff about being outside of the warranty period, make sure you keep stating that it's been a problem since you bought the unit.