BleepingComputer.com: very slow at startup

I have got an Acer Aspire M1641 desktop PC which runs on XP. The problem is that lately during startup the computer holdsup and wont open programs. even though I can move the mouse pointer and click on icons the programs wont open. Also the computer doesnt respond to the keyboard when i press the windows key or any other key. The computer starts to respond after a very long time. Sometimes at startup the computer automatically restarts. Also sometimes a bright blue screen is show with some numbers and text. Another times a lighter blue screen with the windows logo is shown which performs some diskchecking. Would you tell me what maybe causing the problem and how to solve it?

The "bright blue screen" is known as a Windows Stop Error Message, or more commonly called the "Blue Screen of Death (BSOD)". Next time it happens copy down the numbers and post them back here.