My PC won't startup normally anymore. First of all my bios startup takes about 3 minutes after trying to start Windows. While starting Windows eventually, it takes another 5 till 10 minutes before the start menu arrives at the screen. But the whole process takes more than 30 minutes to completely load Windows and all of its services and programs.
During this and after the startup I noticed that the CPU is constanly in use for 100%, while no programs or services use any CPU! Windows will be very very very slow. I even tried to start in Safe Mode but when I choose this option my PC shuts itself down after the selection in the startup options!

My PC is a Dell 8300 Series P4 3,8Ghz HT 800FSB, Windows XP Sp2, SATA 100GB Hard Disk, 1024 MB RAM.
It has always startup very fast without any problems. I didn't install any program and there is absolutely no spam on my PC.

Any idea what causes this problem?

Overheating of the CPU can cause these sort of problems...have you tried to leave your computer powered down for a while and then boot it up...is there any sort of change? Also make sure all fans are working and clean, including those inside the case.

I sounds more like a nasty especially concidering your CPU is at 100%.
I assume you have anti-virus, anti-spyware and anti-aware installed and running . If not download this (http://free.grisoft.com/doc/1),this (http://www.safer-networking.org/en/index.html),this (http://www.microsoft.com/athome/security/spyware/default.mspx), and this (http://www.lavasoftusa.com/software/adaware/). Update them are run them one at a time.

Or update your current software and give it a good scan.
Can you open task manager and see what process is taking up the cpu usage ?

It's also worth checking in the registry (start > run > type "regedit") for spurious entries in the following key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Curr entVersion\Run

I agree w/ Minkey.
If you don't have any of the freeware that he recommended, get some.
More than likely, you have inadvertantly downloaded some garbage (lots by the sound of it) and it is all trying to load when you boot. Spyware, Adware, etc. causes havoc if not kept in check. Do a search on the net for spyware removal, you'll see lots of freebies like Adaware, etc. Good luck with it!:D

AJ

First of all my bios startup takes about 3 minutes after trying to start Windows.

BIOS starts and finishes before Windows. If you have a problem at the BIOS stage, then you either have a boot sector virus (unlikely; these are very rare), or you have a hardware issue. A Windows virus won't affect the BIOS. One way to determine whether or not its an issue with your operating system is to download a "Live CD" (the majority I am aware of are Linux, but I am sure there will be alternatives, just google for them). If the Live CD boots without any problems it would indicated a software issue with Windows. If you still get problems with the Live CD, this would indicate to me that you have hardware issues.

Good luck.

Personally, I would start with the hard drive manufacturers drive utility to make sure the health of the drive is normal.

The problem was fixed while I was investigating the SATA drive on my PC. Apearantly there was something wrong with my SATA-driver?
I switched my HDD to IDE, and after that I got some blue screens while booting XP, but the PC wasn't slow anymore. After several atemps of rebooting I decided to reinstall my Windows and this caused some other blue screens, but I could pass them.

Now the PC is working fine.

Tnx to all for helping.