>Any recommendations as to how to go about solving it? You see, it happens only on some particular machines.

As I said earlier, something is different about those 5 machines. If you want to be thorough, take 1 known good machine and one of the bad machines and compare them directly, in the following order:

- open the cases, check that the video cards, network cards, motherboard revisions and other parts are the same make/model and revision. Make note of the make/model/revision of all parts, you will be looking for updated drivers later

- check for available motherboard BIOS updates on the HP web site; apply if available

- go into the BIOS setup of each machine, make sure that the settings are the same. For example, you may find that "Plug & Play OS? Y/N" is set to Y on one machine (which is correct for all OSs W98 and later) and on another may be set to N.

- boot Windows, go into Device Manager and compare driver versions for each component. If any devices are not properly installed, resolve the problem. If you find a difference in drivers, update the problem machine with the latest available driver(s) from the vendor web site. Be sure to use the driver that is exactly correct for the hardware make/model/revision you noted earlier.

- install all critical updates from the MS web site: http://windowsupdate.microsoft.com. Consider updating to IE6 with all patches if you haven't done so already.

- check that the same programs are running in the background (Ctrl-Alt-Del as I pointed out earlier). Also check programs that are running at startup in the following locations:

CONFIG.SYS
AUTOEXEC.BAT
LOAD=, RUN= values in WIN.INI
Registry entries in HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run and ...\RunServices, and the equivalent key(s) under HKEY_CURRENT_USER
Programs in your Start Menu...Startup folder

- closely check antivirus configuration. Try running with real-time scanning disabled on the problem machine(s), to see if that makes a difference.

- is there anything common to the 5 machines not common to the ones that are OK? Are they subject to low electrical voltage or brownouts/spikes? Are they on a common network hub/switch that may be faulty?

- are you certain the users are not running unauthorized programs like games, instant messaging, etc.?

If you have gotten this far, you will probably have found one or more things that are different between the good and bad machines. It's a lot of work to go through all these steps but it's the only way to track down and eradicate intermittent problems. You are lucky to have good machines to use for comparison.

Good luck.