Computer help!?

help! everytime i switch my moniter on it always says it found a trojan horse, i delete it permenatly, shut down my pc because it goes so slow afterwards, then, it works fine, then the next time i go on again, it says its found one again, and again and again. I scanned the pavillion, recovery, and local disk, deleted everything, scanned my computer for spyware, removed them, restarted my pc, and it still popped up, i dont see what the problem is, i have firewall, avast! anti virus, spyware begone. Help would be apprechiated, thanks x

Computer help!?computer repair

Scan your PC in safemode. This is how to get into safemode.

For Windows XP

If the computer is running it is best to shut down Windows and then turn off the power.

Begin by first clicking on the Start Button and then click on Turn Off Computer.

Now click on the Turn Off red colored icon to shut down your computer system.

It is best to wait between 15 to 30 seconds before you turn your system back on.

Turn on your computer and start tapping the F8 key on your keyboard.

Some Computers may display a keyboard error message if you begin tapping F8 too quickly.

Restart your computer again and begin tapping the F8 key a brief second or two later.

When the Windows Advanced Options Menu appears, Choose the Safe Mode option and hit Enter.