Our laptop computer will TOTALLY freeze up at unpredictable times, and
must be restarted by turning the power off and on.  This happens
typically once or twice a day, but can sometimes be as frequently as
every 5 minutes.  The computer is an AMS Roadster 151CT with 64 Mbytes
of RAM, purchased in March, 1999. The operating system is Windows 98
SE.  Main programs used are Outlook Express 6.0, Excel 97 SR-1, and
Windows Explorer 6.0.  Norton SystemWorks 2002 version 5.0 is
installed, has virus updates, and scans the computer periodically.

We had a similar problem back in 2000.  After unsuccessful repair
efforts and even a complete reformatting of the hard drive, it was
suggested that there might be a mouse incompatibility.  So we
installed a new mouse driver and the problem sort of went away. 
However, we've only intermittently used the laptop since then, until
we recently resumed heavy usage and again experienced this problem. 
So we installed a new Logitech optical mouse and software, which
helped for maybe a week; then problem resumed.  Reinstalling the
Logitech software didn't help.

What is the likely cause for these freezes, and what can we do to stop
them?

I'm not a reasearcher, but, this is what I would do if it were my
problem:
1) I'd make notes of exactly what I was doing when the computer
freezes(what was running, whether it be in the background or whatever.
2) I'd see if I could re-create the situation, going from the notes
indicated in item #1
3) If I could re-create the problem, I would then start to shut down
the running processes one at a time to see if the problem keeps
happening or goes a way, of course I would note, what was running and
what wasn't(what program I 'killed') "process of elimination"

NOTE: I have heard that people have problems with the power saving
stuff, so you might even want to turn that part off(in control panel)

hope some of this info. might help..good luck

There are many things that can make a computer behave in this way. One
factor could be that your drive has developed bad sectors and can't
read over those sectors when accessing. It would be a good thing if
after you formatted the drive and installed only the OS and Norton
Systemworks, you use NDD to verify that the drive has no bad sectors
or identify them if any. Once identified and fixed, you can then
install whatever programs you need.

Feilong (Google Answers researcher)

Dpwiener --

Feilong-GA has made some logical suggestions for the cause.  Myself,
I'd vote for a loose connection somewhere in the power or system bus. 
I'd try disassembling the system, if you're handy with a a
screwdriver, and re-seating all connectors and components: hard drive,
socketed components, connectors.

Your problem could be cause by a large number of things, including
defective memory components; stiction in the hard drive; loose
connections; power supply failures; and even software.

Best regards,

Omnivorous
Google Answers researcher

Thank you all for your suggestions.

Houstonguy, I'll try noting what processes are normally running.  But
of course I can't be sure what's running at the precise moment the
computer freezes, since there's no way to recover except by cycling
the power.  Regarding power management, the computer is set to "always
on" (except for the hard drive, which had been set to turn off after 5
hours; I've now changed that to "never turn off" as well).

Feilong, I just ran Norton Disk Doctor and everything came up okay. 
Now I'm running a disk optimization, so we'll see if that helps. 
Obviously the last thing I want to resort to is reformatting my hard
drive.

Omnivorous, I'm very reluctant to open up the laptop and fiddle with
components (even though I'm an electronic engineer).  The risk of
damaging something is probably higher than the hope of fixing
something, unless I'm first able to isolate (or at least narrow down)
the failure location.

My own guesses as to the source of the problem would be (1) an unusual
hardware-software conflict, or (2) software incompatibility between
two programs.  I'm hoping that someone might have experience with or
knowledge of similar problems on other computers, and can suggest what
software could be responsible or how to go about identifying the exact
cause.

Again, I sincerely appreciate your comments.

Dear dpwiener-ga,
(I'm afraid I don't know your real name),
I have read your question and the accompanying comments. I believe
that either your hard disk or the memory chips are faulty. As your
laptop is pretty old (1999), it is quite likely that your hard disk is
the culprit. Does scandisk report bad sectors and does the number of
bad sectors go on increasing day by day? If so, you must replace your
hard disk.
If you are sure that hard disk is fine, the memory chip may be faulty.
To find out if this is the case, you can use various softwares that
test your RAM chips.
Alternatively, you can limit your RAM and see if the problem is
solved.
Start --> Run --> msconfig --> Advanced
In the "limit memory to" box type 32. This way, windows will only use
32MB of your 64 MB RAM chip. If the problem is solved, your memory
chip was faulty. Try the smallest allowed number first.

Caution: Be sure to enter a proper number in the memory box. I think,
16 is the minimum. If you enter a number less than 16, windows won't
start and you will have to restore the registry using a startup
floppy. Avoid that. To find out which number is valid, click on the
"?" button at the top of the "Advanced" window, (your mouse cursor
will turn into a question mark) and then click on the words "Limit
memory to"
Best of Luck!!!!!!