Normally I have the pc on all day and nothing happens until last week when I returned from work and tried to use the pc and it was frozen It did not respond at all so I have to turn off and then on so it worked fine. When I am using it all is fine but when it is not in use after a half hour it frezees so in the morning when I turn off the win log appeared and it stayed frozen until this moment. What could be the problem. I cleaned the disk,ad-aware,spybot but the problem repeats.
rgds
mloo55

Some program that's running in the background has developed what is called a "memory leak." This is especially critical on machines where there isn't much memory to start with, and is a problem with all operating systems so far as I know, but worse in some than in others. Memory leak is an inaccurate term because what is really happening is that a program is using memory, and when it's finished with what it's doing, it's supposed to release the memory it's been using. But it doesn't. Then it does it again, and again does not release the memory. It could be something like Norton's Live Update checking for updates. On older versions of Norton, when you removed the software to install a newer version or a different antivirus, Live Update would be left behind, needing to be uninstalled separately. Running in the background constantly, it would never be able to retrieve an update because the main program was gone. It's really hard to pin down what program might be causing it, or why it isn't happening while you're using the computer.

This is one of the reasons that it's good to do a clean install of Windows 98 every so often. But there's no guarantee that it won't happen again.

Stop doing what you're doing that causes the problem.

I know that sounds over-simplistic. (sorry about that)

First off, you said that you leave your computer on while you go away.
You should NOT do that. Those things do catch on fire, you know.
I've seen computers that caught on fire.....It ain't purty!
There's also three other things it's doing while you're away,,,it's drawing electrical power and running up your electric bill,,,it's generating heat that it then has to try to get rid of,,, it's sucking in dirt, that will clog up your cooling mechanism.

Secondly, if you've not cleaned out your PC lately, it may just be loaded up with dirt, in the CPU cooling fan and heatsink, the PSU and in the air vents. If your processor chip gets too hot, it will just shut down. Clean it out.

Lastly, there IS indeed a condition in windows 98 (more than XP) called a memory leak.
The only way to get wasted memory back is to do a re-boot on your PC.
Even during booting up, some things will run for just a few seconds, that will never give you back all the ram that they used. Then as the day goes on, the problem just gets worser and worser!
After a couple of days of being left on, your little computer will have NO ram available at all.
Then everything has to run right off of the hard drive, slowing your system down to a crawl.

Computers that absolutely HAVE to be on 24x7 to receive faxes, support a network, etc., should have extra cooling fans installed and be cleaned on a regular maintenance schedule. They should also be running a memory management program like "MemTurbo" to keep the ram refreshed and overcome the old "memory leak". They should also be on a commercial quality Surge Suppressor and battery backed up Power Supply (UPS).

Good Luck,
The Shadow