My computer will freeze up/lock up every seconds at login

Help! My computer that I've had since '09 has been freezing up every few seconds at startup, for example, the start button glows on mouse over and when i click the start menu doesn't come up, then if I move my mouse the windows logo is still glowing, same goes for the notifications triangle. Other items would freeze too, such as the wifi icon in the notification bar and gui items on my running programs.

My computer defragments itself every Wendsday (btw, does it defragment itself if it's logged off?) and I'm afraid of clicking on something in the fear of it locking up on me! It also studders my games (but I don't have a low frame rate) and freezes Steam VERY ofter (although, I think that's just a problem with Steam)

Specs:
Intel Core 2 Quad clckd @ 2.83 Ghz
Windows 7 Professional 32 bit
2 GB of ram

nothing?

Carolyn said:

When did you first notice the problem? Had you made any changes to your computer around that time (add/remove software or hardware)?

What security programs are installed? Have your run any scans to rule out malware?

I'm not sure when is started (I guess when I got the computer) but I did notice that the problem significantly increased after I upgraded from an Intel Core 2 Duo to an Intel Core 2 Quad. I also had a full version of Windows 7 before it was released, then I went to Windows XP, then back to Windows 7.

I have the Microsoft Security Essentials suite installed for security, and I have scanned for malware, with results turning out negative.

Carolyn said:

Does this only happen at start up, or does it continue to happen while you are using the computer?

It happens a lot for about 5 minutes after start up, and then after that it would randomly freeze on me about every 10 minutes or so.