Strange pause in Win2000 every 4 secs

A friend gave me a notebook (HP Omnibook 6100) with Win 2000 Professional on it to disinfect because two instances of the Haxdoor Trojan had thrown the combo of Trojan / Antivirus software into a loop of discovery - deletion - reinstallation - discovery... during log-in, so the system didn't boot anymore. I removed those Trojans using Insert (Linux Live CD) and the system now works fine again, various scans with different programs report no malware whatsoever anymore.

However, there's one problem: about every four seconds there's a pause of a fraction of a second, which lets the mouse skip and typed letters disappear; this makes the system almost unusable, as you always have to control what you're typing. I lose about about one in five letters at my rate of typing. This applies even before login; as soon as you can move the mouse it skips every four seconds if moved, and when I enter the user password letters already get lost.

I had a look at the processes in Task Manager and found that when I am doing nothing the System process (not System Idle) with PID 8 gets active in about the same rhythm as the pauses; and using Process Controller 3.0 from k23Productions, I found that thread number 18 in that process is responsible for the activity, but as this is a system-critical process I can't do anything about it. Its priority is set to normal.

Now I'd still be willing to suspect some malware, but then I tried a Win XP-based Live CD made with PE Builder, and that showed the same behaviour. Now I'm baffled.

It's not the hardware either, as the notebook performs perfectly when a Linux Live CD is booted. I did try to disable Power Management in BIOS, which is just about the only thing I can disable which isn't strictly necessary, but that didn't change anything.

I've searched for information on the System process (which seems to get confused with System Idle half the time) and its 18th thread, in the hope that there is consistency among instances of Win 2000 as to which thread does what, but I couldn't find anything useful.

Does anyone have any idea what I could do next?

Robin

 

Solved: using Process Explorer (www.sysinternals.com) I found that ACPI.SYS caused the problem, and on the HP support forum I was told that a defective battery could cause it. And indeed, the battery is dead, after removing it the notebook works perfectly.

Robin