System hanging/freezing in DOS

Over the last several months, my father's Win95 (OSR2) system has been freezing up more and more frequently, with no recourse other than the reset button. (Prior to that, it had run for a year or so with no problems.) At first it happened only once or twice per day, and I suspected software, since he had recently installed McAfee Office. But after removing all traces of McAfee, the hangs continued. They seemed to be uncorrelated with whatever was running or being done on his system. They grew more frequent, up to 10-12 times per day. So a few days ago, I took it on myself to perform a clean installation of Win95.

While I was fiddling around in DOS, preparing to reformat his C: drive and so forth, the system hung again. I was able to reproduce the hang pretty reliably (although not every time), just by using the EDIT command on a simple .TXT file and pressing the Page Up/Down keys several times in quick succession. Now thinking it might be a problem with DOS itself, I booted his system into DOS using a startup disk created on my own Win95 OSR2 system (with no extraneous drivers or TSRs in memory). Alas, the hangs continued. So now I began to suspect hardware.

We have installed a new mouse and keyboard, and I've deinstalled all add-in cards except his video card. This has relieved the symptoms, but I have still gotten his system to hang by editing a simple text file (and at least once by just leaving the system idle at the C: prompt). The remaining hardware is:

- Amptron PII-2000 motherboard with an AMI BIOS
- Pentium II 266MHz CPU
- 64MB SDRAM memory
- Diamond FireGL Pro 1000 AGP video card
- two hard drives: a 5.7GB Maxtor drive and a 6.4 Western Digital drive
- a Digital Research 40x CD-ROM
- an Acer 4x4x32 CD-RW drive (removing this drive didn't seem to help)

By process of elimination, it seems as though the problem must be something on the motherboard (e.g., the IDE controller), the CPU itself, or memory. How can I troubleshoot these components, or do we just have to spend the money to replace them on a trial and error basis?
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i would suspect memory first.  do you have any diagnostic software, like qaplus?  see if you can get ahold of some software to check your memory.
It doesn't hurt to remove & reinstall every cable and memory stick on the motherboard.  This can alleviate an intermittent connection problem.
drlivingstonAuthor Commented:
I ran all of the memory tests using an old version of AMIDIAG (4.50), and it found nothing wrong with the memory.
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Are all the fans running. Is there a thick layer of dust covering all the components and inside the power supply. Could be overheating and the chips could be permanently damaged. It now takes less heat to kill them.

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I have to agree that this is either a memory problem or possibly heat related.

drlivingstonAuthor Commented:
There was some dust inside the case but nothing too excessive. I don't think it's heat-related; all of the hangs (except for one time it hung at the C: prompt) were associated with specific keyboard (in DOS) or mouse actions (in Windows). Generally, if I'm in DOS and just typing a command line at regular speed, or executing most commands (e.g., TYPE, MEM) there's no hang. The only reliable way I've found to get it to hang is to EDIT a file and then page up and down quickly. (There may be other ways, too; I just haven't explored for others since this one "works" pretty reliably.)
In the bios you can change the typmatic speed to see if it might be a bios problem

hope this helps
drlivingstonAuthor Commented:
Well, if it were a snake it would have bit looks like joed's suggestion was on the mark; the fan wasn't working any more. No wonder the system behavior was so erratic. I'll be replacing the fan tomorrow morning; hopefully no significant damage has been done (other than the long hours I've put in troubleshooting this one).
Was it the processor fan or the power supply fan?
drlivingstonAuthor Commented:
It was the processor fan - plain as day, except I just didn't notice it. I replaced it this morning and everything is back to normal. Thanks for your suggestion - and thanks to everyone else for their helpful comments as well.
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