Mysterious Speedup and Slowdowns

[Hengist]

This problem started about two days ago. I made no obvious change in system configuration or installed programs. When first started, the system runs perfectly fine. However, within a few hours, the system enters a pattern: the system will mysteriously halt, followed by a burst of activity, and will then start again.

More specifically, the programs in use will become non-responsive. The mouse pointer will still move, but the desktop, taskbar, start menu, and the loaded programs will stop responding. The ceasing-of-response is sometimes partial: sometimes a program will remain semi-functional, with freezing occurring when certain (seemingly random) parts of the program are used. During the system slowdowns, the hard disk drive indicator light blinks briefly exactly once per second. If the task manager is open and remains functional during the slowdowns, no increase in CPU, network, or memory activity is noted.

After about ten second of slowdown, there will be a two or three second period of sustained hard disk activity. All of the things that I tried to do during the slowdown will occur at high speed. Then the system slows down again.

I have already scanned the system for spyware using Malwarebytes Antimalware, Spybot S&D, and Avira Antivir. I've also run CCleaner. Any ideas? System specs are below.

OS Name: Microsoft Windows XP Professional
Version: 5.1.2600 Service Pack 3 Build 2600
System Type: X86-based PC
Processor : Quad Core2 Q9550 @ 2.83GHz
BIOS: American Megatrends Inc. 1306, 8/20/2008
RAM: 3.2 GB
Available RAM: 2.8 GB
Virtual Mem: 2.00 GB
Video Card: NVIDIA GeForce 9800 GTX+ (Latest Drivers as of last month)
Motherboard: Asus P5Q Pro (Latest BIOS as of last month)

 

[montyuk]

any errors or warnings listed in the event viewer?

 

[Hengist]

Yes, under System. Unfortunately, though, they are not operating system warnings. They are warnings from Avira Antivir; when opened, the message is: TIMEOUT<$progname> $filepath, where $progname is a program and $filepath is a path to a seemingly random file.

I looked up the meaning of the error on Avira's site. According to them, TIMEOUT errors are generated when a file is too large to be scanned quickly, when the system is too busy to quickly service the Antivir System Guard, or when the hard disk has not responded to the read request in a timely fashion.

 

[montyuk]

may i suggest switching to the free version of avg to replace it?