Studies have shown that the average computer can hold about four times it's internal volume in hair and dust. Additional studies are needed to determine how they do this.

Just don't use a vacuum cleaner (either the normal end or the exhaust end) to clean it out. Vacuums are notorious static electricity generators and can easily fry a computer.

Go to http://www.ubcd4win.com/forum/ and post the question there. They actually now about computers and stuff.

I have fixed a computer in an auto-body shop that wouldn't even turn on by simply blowing it out with an air compressor. Dust has got to be one of the leading killers of computers (laptops especially).

In our house, its not dust that kills laptops, its the two 1 year olds that treat them with the respeat they don't deserve! At this stage cheap laptops are the way to go for home use. 3-500 bucks or pounds gets you a lot of run time. Just back up stuff and treat laptops as throw aways and your golden.

Compressed air cans, and many vacuum cleaners for that matter, don't remove dust but just move it around.

Dust is somewhat conductive so as it coats the surfaces in a computer it can "short" exposed traces or wires. There should be no permanent damage once the dust is removed.

Be careful not to use too much suction or compressed air pressure. You don't want to suck a wire or jumper out of a socket!

Too see some really dirty pictures (of computer innards) try this story from an IT industry publication: Dirty, dirty PCs: The X-rated picture guide.

Safe computer cleaning tips I've collected from various techs:

Don't spin fans with compressed air. You can spin them past their designed speeds and damage them. Hold them still when blowing them out.

A soft round paint brush is great for corners (and keyboards). 1/2 inch or 1 inch work best.

Use puffs of compressed air to dislodge dust and debris. Hard blasts could drive it deeper into where you don't want it.

Vacuums are dangerous to computers, both through suction and possible static. Blow and brush everything out of the computer, and vacuum it up after you've moved the computer out of the cleaning area.

Which is why I take the work pc's out back and use the SCBA bottles that are under 1500psi (our allowable low for SCBA use) to blow them out.

Squeeky clean.

With computers getting them clean-room clean is usually a waste of time and money. It is also potentially hazardous. In an hour of run time they are going to show some dust anyway. Go for a solid 85% or 95% clean and call it good enough. I've seen people damage circuit boards worrying the last specks of dust out with compressed air, brushes and swabs.

Cleaning more frequently to a lower standard is better than getting it 'really clean' once every decade. The $5 cans of air work fine but you still need to practice restraint. You can use a brush but gently, gently. Being a barbarian, and heretic, I use an industrial air compressor at 120 psi and keep the nozzle about a foot away. Good advice on restraining the fans from Compugeek.

Yes, if you do it inside you're just shifting the dust around. No big deal if the PC isn't too dirty. Next time you vacuum and dust you get most of it. If the PC is really dirty blow the dust out outside or arrange a fan to blow the dust out.

If after you clean the PC it beeps at you or fails to start first time open it up and examine it carefully. Don't just keep restarting it. Check very carefully to make sure the heatsink/s are seated properly, that all the fans are still connected and running. That the memory, cards, and all connectors are seated firmly. Look for foreign objects that might cause a short and if the mounting spacer might have collapsed or fallen out allowing the MB to short out against the back plate.

PCs have come a long way in protecting themselves. I caught a motherboard with a paperclip that got picked up during cleaning and caused a short. That sort of issue used to be the death of a board. This time the start-up pre-test caught the short and shut the process down before any damage was done. The guy would hit start and the lights and fans would start and then it would beep a couple times and turn off. Good thing he brought it to the shop after just a couple of tries. I remove the paperclip and it ran like a champ.

A heatsink that gets banged loose is another common fault. The CPU overheats after a few seconds and shuts the PC down to protect itself. Keep trying and eventually the CPU fails. Reseat the heatsink and all is well. Some CPU/motherboard combinations are self protecting. More and more are these days. But a few don't. It is a feature worth having.

They don't always protect themselves but PCs have got a lot tougher over time.

If you use canned compressed air (e.g., "Dust Off") don't shake the can or tilt it sideways or upside down. Otherwise you'll possible send liquid out when all's you want is air.

Alex was right -- the monitor was dying. My friend came back from Mexico and said so. I know she was right because she always is (and keeps telling me so).

The new one (El Cheapo) works fine. There are several leftover parts, but I guess they were redundant. Funny how the little folder of instructions said if I was having problems to put the help CD in for further info... If it wasn't working, how would I read the CD?

Anyway, thanks for all the info.

Sue