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My CPU usage is very high by default. As soon as I starts a program it touches the maximum. After some time it becomes normal. I have a doubt that my disk is infected. So I tried to install MalwareBytes and Kasperkey to scan it. But they consume most of the CPU.

My entire system hangs and I can't scan my system. It restarts some time. Can anybody suggest me a solution for this? And can anybody suggest me a lightweight antivirus suitable for a Pentium 4, 2.4 GHz, 1 GB RAM running Windows XP Service Pack 3?

The problem still persists, here is the print screen of process explorer. enter image description here It's showing 96-100% cpu usage by interrupts. My machine is crawling because of this. Can anybody give me a solution?

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Use the Task Manager to find out what process is using most of the CPU... My primary guess is a virus. – Breakthrough Aug 29 '11 at 13:47
I tried it. But as I have mentioned, most of the time the program last started, consumes most of the CPU. eg. If I start my task manager to check the CPU usage, it starts to consume 60-70% of CPU for few seconds and than it becomes normal. Same with firefox. – narayanpatra Aug 29 '11 at 13:52
If you need a decent AV, go with Microsoft Security Essentials. Free, fast, and made by the people who made the OS. – Breakthrough Aug 29 '11 at 14:12
Also, start Windows in safe mode and do the scan. – Sathya Aug 29 '11 at 14:43
It's not necessary to use safe mode for scanning a system that has two virus scanners installed. – Tom Wijsman Aug 29 '11 at 15:05

There are three explanations for your problem:

  1. Heat. If your CPU is getting hot, it will throttle. With fewer working cycles available, everything will take much more CPU time to get work done. It could be that your CPU fan failed or the thermal interface material cracked due to mishandling.

  2. Malware. Malicious programs can increase CPU use. If you can't anti-virus programs to work reliably, use a boot-able anti-virus rescue disk. Kaspersky is works well, as do many other free ones.

  3. Drivers. Some hardware drivers cause CPU problems. Make sure all drivers are up to date.

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Edited the question. Kindly check. – narayanpatra Sep 6 '11 at 7:21

Your concern is unclear and actually could be normal behavior, depending on your system.

Your CPU should clock all the way to 100% regularly. If it didn't, you won't need such a fast one! It used to my job to make sure CPU usage was 100% as often as possible :)

Whenever a program is busy doing something and it not waiting for another resource, it should keep you processor completely busy. If it does not reach 100%, that is because it is waiting on other resources like memory or disk I/O.

So, it sounds like your programs do some processing on startup and then go on to wait for your input. If that was NOT the case before, your programs may have been hooked so that they call a new DLL on startup. This happens with legitimate programs like Google Desktop but can also be used by anyone else. There are registry entries that control which foreign DLLs are loading each time a program starts. Consider if you've recently installed something with a global behavior like an Antivirus for example.

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Edited the question. Kindly check. – narayanpatra Sep 6 '11 at 7:21
That is very unusual, I would suspect a driver issue OR faulty H/W. You'll have to try a couple of things: (1) upgrade all your drivers, (2) remove all non-essential H/w, (3) uninstall drivers. If you do this one by one with a reboot it between you may find the culprit. – Itai Sep 6 '11 at 13:22

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