I have a Gateway laptop that shuts down right after booting. I've taken it apart and
 

I have a Gateway laptop that shuts down after it boots. Sometimes it will get me online and I start doing something and the screen goes black after about 10 minutes. Sometimes it goes black quicker (before I even get online). I took the computer apart and cleaned it, because I know it overheats. I also use a laptop cooling system and aim a Vornado fan right at the laptop. Still I get the black screen and I never know when it's coming. Any suggestions? What should I look for in the BIOS settings? What is an HDD? Thanks!

Where in the boot process is it when it shuts down?

Try booting to a live CD (Slax or Knoppix are good for this) and taking a look at your HDD.

Check the BIOS settings.

Based on the extremely limited minuscule amount of information which you provided, I'm inclined to suspect that the HDD is bad or corrupt or that the HDD disk controller or connections are malfunctioning.

Taken it apart? Everything seems to be working? How do you know?
If you boot and go into the BIOS setup screen, does it shut down as well?

jlinkels

In addition to frankbell's suggestion, can you confirm the battery is fully charged. Are you running it on battery or mains? A low battery charge would cause shutdowns if it was the only power source.
15 seconds is probably too short a period of time for an overtemp shutdown. I'm thinking blocked air vents, dodgy fan, but you could check that.
Is anything being displayed when it shuts down? For that matter, does it shut down properly or just die?

As jlinkels, having taken quite a few laptops to bits, I've never been able to tell they were "working" from doing this and looking at the various chips, caps, connectors, etc. What do you mean?

Give us some more info to go on and welcome to LQ!

Play Bonny! :hattip:

Take the fan off the heatsink on the processor and clean the dust out of it. I've had to fix a couple Intels doing the same thing.