Archived from groups: microsoft.public.windowsnt.misc (More info?)

I hope someone can help me with this one.

I'm running Windows NT 4.0 with SP6a as a development system with Visual
Studio 6 & SP5 and a few other tools. This system has been working well for
several years until the past few months.

Recently I've started having problems where Explorer won't open ANY
application. After a reboot/powerup, it works fine, but after a while it
stops working.
- I can't double-click on icons,
- I can't Right-Click and select Open - though I can do other right-click
functions like Rename, Edit or Copy.
- I can't place the cursor over an icon and press the Enter button,
- I can't open Windows Explorer - select an exe file and press Enter or
click on it to start.
When it fails, the only way I can start any program is to use Start buttton,
Run and enter the application name (or Run via TaskManager).

The only recovery is to reboot the system - though recently I found that I
can use TaskManager to kill Explorer and then use Task manager again to
restart Explorer - this seems to restore the system. However the problem is
only solved for a short period of time. Initially when it started several
months ago, I could get weeks between the problem. Now it seems like I'm
lucky to get a day or two. Sometimes it will happen more than once a day.

Generally the only apps I'm running are: VB6, VC++6, Windows Explorer,
WinDiff, UltraEdit32, EditPad and our application developed using VB&VC++
(VB EXE, VC&VB activeX controls, and device driver). Our app has existed for
years, but we continue to enhance it, etc. I haven't added any new apps to
the system in the past year.
Sometimes it can be as simple as just Windows Explorer and VB just sitting
for a few hours and then the problem will occur. Or it may not happen until
I've launched, closed, re-opened, etc several times all of the above
programs. It's not consistent what causes the failure.

I've run several different and recent virus scans on the system, though it
rarely ever has access to the internet (and it has several additional layers
of protection).
I've checked the EventViewer and don't see any errors when the problem
occurs.
Resources seem to be well within normal limits for this particular system.
I checked the registry for EXEFILE entries to see if something got/gets
changed.
I've tried to logout and log back in as a new user, but this doesn't clear
the problem (so apparently it doesn't restart Explorer).
I've re-installed Service Pack 6a in case any obvious OS files had become
corrupted/damaged.

I've checked MS KB, MSDN and TechNet but couldn't find anything on this (and
I tried a variety of keywords).
I've done a general search on Google without success.

One thing I have not yet tried is a thorough memory test, though I have set
the BIOS to do its more extensive test and it found nothing. I'm still
trying to find a good test program which I'll try in case there's a small
amount of memory that's failing.

So far, I haven't found any info about a similar problem and how it was
resolved.

If anyone has any ideas on the cause and/or how to solve this problem, I
would really appreciate it. It's starting to seriously slow down my work.

Thanks in advance for any info you can provide.
cheers,
Don Pullen