Computer help

[Mareeps]

Okay, so I usually leave my computer on overnight. I know the computer can handle it, since it's done it many times before. But, if I don't have internet open, the computer just shuts itself off. Any way to prevent this?

Also, sometimes when I turn on my computer, the computer tower makes a loud, revving noise. Any idea what's causing this? Unplugging it and plugging it back in seems to fix it.

[Slime Slayer]

Does the inside of your computer look like this?
http://www.retrouprising.com/img/2012_04/133.jpg
Maybe it's over heating and needs a good cleaning?

[Mareeps]

Might need to have the inside dusted off, but I always feel like i'm gonna break something if i take it apart to clean. But that don't explain why the computer shuts off automatically if I don't have the internet open.

[KATZ]

check your settings in the control panel, it may have an option for shutdown after so many minutes of inactivity, id check it myself but i do believe you said you were running XP before, which i dont have, but ill see if 7 has it

EDIT: 7 has a sleep mode, so maybe yours has a shut off

[Dudebro]

Yup sounds like you have a sleep/power saver mode setting on. You should be able to make just go into sleep without shutting down, it'll shut down the monitor and you have to click the mouse to wake it up.

Yup again, sounds like your fans/vents are clogged. Go buy a can of compressed air for like 2 bucks and blow it in there. Your PC should have a pretty simple way to open it. If you can't figure it out you can google the brand and make of it and there should be instructions online. Unplug it before you do though, then once it's open just blow all the dust out. Hold the can upright so it doesn't get cold and leave that nasty film on your PCs private parts. Basically just read the directions on the can.

[SMASH]

sounds like it might be overheating and the fans are dirty if it is shutting off and sounding like it is reving. open the case up to identify where exactly the sound is coming from.