Almost non-working computer (logs included)

Please help me with my problem with computer.

Problems started few days ago but the day they appeared nothing was installed or changed in the system.

Currently the system (Windows XP, Service Pack 3) works as follows:
- before the desktop appears it takes about 3 minutes with black screen and only cursor on it
- after desktop appears, it takes about 5-10 minutes of processor working before any program can be run
- then programs can be run instead of my browser (newest Opera) - after opening it takes another 10 minutes of processor working before anything may be clicked
- exploring any websites is often interrupted with another minutes of pause with processor working

Computer has NOD32 installed and shown no threats, but some other programs (Arca MicroScan) shown some trojans.

Additional info:
I am from Poland so please forgive any mistakes I could have made in English. I installed all programs from Your site, but still there may be some lines in logs which may be in Polish - I could not do anything about it, so I hope that it will not be a problem for you...
ComboFix prompted me to disable NOD32 but all attempts to do so (expept complete uninstalling it) failed - I really do not know why...

If you have any ideas how should I proceed, please help me.
Thank you.

 

Sorry for delay in replying.

As I do not have Internet Explorer on my computer anymore (I uninstalled it long time ago) I first tried to run the metnioned antivirus scan on my laptop.
I did it because with my current state of computer it will take even few hours before getting IE and this scanner working.

I read all FAQ's and troubleshooting on the site but still get only information that scan failes because I did not buy license (strange, because it clearly states that it is a free scanner).
I attach the message I get to the post. Maybe you have any idea what may be the problem.

Additionally, if it is not a malware problem, what may be causing these problems? Will trying to use restore point or reinstalling windows (which I want to avoid) help? Or there are other helpful solutions you would recommend?

PS. Arca MicroScan (the program I mentioned in post before) detected Heur.W32 on my computer. May it be a cause of these problems or was it a false positive?

 

Unfortunately, my computer stopped working at all.
Some information about registry missing (on blue screen) and Widnows was unable to load in all modes and using restore point did not help, too...
I even did not have a chance to visit the website you suggested. Nevertheless, thanks for your advice.

Now I am formating system drive and installing Windows again.

Hope it will help...

 

Actually reinstalling did not help.

I had to give my computer to professional service.

The cause of the problem was a the faulty hard disk. It had lots of bad sectors and cannot be used anymore.

Thread can be closed. I have new hard drive and everything works fine.
I am writing in case anybody has similar problems and also finds out that malware is not a problem...