computor shuts off

Help!! My machine shuts off without warning while using or while remaining on without using (ie. over night) There is no specific on time when this occurs. Can use 2 to 3 hours with no problem then bang, off she goes. If I leave it off for a while, (cool down) then re-start, I'm good for awhile. WHATS HAPPINING!! Can anyone help? My unit is HP 6640C, Windows 98

 

I'm guessing you have an overheating component, most likely a power supply. I would first swap the PS with a known good working unit. An overheating CPU or component on the MB can also cause this, but they usually cause a reboot not a complete shut down.

 

I agree with Trinitro, sounds like overheating.
I recommend getting can of compressed 'air' and blowing out interior of your PC.
Take PC outside and remove side panel.
Use compressed air to blow dust off motherboard, riser cards, ledges and anyplace else that collects dust.
Heat sink/fan of CPU,,,, be generous blowing these clean.
Case fans and exhaust fan of power supply are also good places to blow clear.
Replace cover and reconnect cables.

Try to place PC in area gets good air flow.

Bluecanary25

 

Make sure you turn the computer on for a few seconds to make sure the fan is blowing on the CPU after you blow it out. If your computer is the type that starts and won’t let you shut the computer right back off before it post's then let it boot and shut it down. What I am getting at is make sure fans are running. You might consider going to a better CPU cooling fan. I use a "Golden Orb" from http://www.thermaltake.com/ keeps the CPU in this 933 at or below 102 deg F` with multiple apps and a game running. I also have a 2" pancake fan blowing over the memory and video card. Heat is the enemy of anything! There are dozens of after market cooling products for computers today. From fans to actual refrigeration units that run's R134 coolant like in your car AC over the CPU. The guy that actually hit the 1 Gig CPU mark hit it with an AMD 500 processor cooled to below Ø Deg F`.

 

Heat is most certainly a primary suspect to include dust buildup. Another possibility to consider is a short or bad grounding on the motherboard. Shorts may crowbar a power supply voltage and shutdown the system. Heat causes expansion. A couple ways to check for this type of problem is:
1) Make sure screws securing Mother Board are tight.
2) While system is up and running, lightly tap or press on Mother Board using the plastic end of a screwdriver to see if it will shutdown.

 

I had the same problem on my HP that was 5 months old. It finally got to the point where it would shut off with 8 minutes of use. I then started getting the warning message that the hard drive was failing. HP replaced the hard drive and I have had no further problems.