Windows suddenly freezing at startup

Hello all. I have been a happy Windows 7 user for around 3-4 months now, and just today I encountered a problem. Whenever I boot up the computer, it would freeze after startup. Sometimes it would freeze at the welcome screen, with the little loading circle in the middle stop spinning. Other times it would freeze after my desktop is loaded with all the icons and as some of the taskbar icons start appearing in the bottom left. Again, my computer has been running Windows 7 fine up until today.

My specs:
OS: Windows 7 Ultimate (not sure of exact version/build)
Mobo: Asus P5GD1 Pro
CPU: Intel Pentium 4 3ghz
Ram: 2x1GB
GPU: 9800GT

It's quite an old system but it has done the job fine until now.

Things I have tried:
-Going into safe mode (this works fine but I don't know what to do there)
-Going into event viewer (I find a few critical errors but they were all about a bad reboot etc.)
-Going into device manager (no yellow exclamation marks or anything)
-Using the chkdsk command in cmd in safe mode (no errors or anything)
-Using the repair manager thing on the windows 7 DVD (no errors)
-Using the memory test on the windows 7 DVD (not sure if any errors, when I came back it rebooted and was frozen at the desktop)
-Taking both ram slots out and putting both back in
-Taking one ram slot out and booting with only one

So, anything else I need to try before I try reformatting?

PS: I've actually managed to get into task manager before it freezes. Both CPU usage and physical memory are at about 24% when it freezes. I dunno what that means but hopefully it's useful in finding the problem.

It could be heat - you have enough cooling in that case?

First off, thanks for all the replies!

K3VL4R said:

It may have a been a recently installed program or corrupted start up program or device. So you could also try to load a system restore point dated before this issue started happening and that would tell you if that is the issue.

Unfortunately I don't have a system restore, I've never been a user of one, not really sure why. However, a couple of days ago, I changed my AntiVirus from Eset to Avast. Dunno if that would be a problem but perhaps I'll try uninstall Avast in a tick. However I have disabled Avast from startup as the first time I saw the freeze, it froze when the Avast icon popped up in the taskbar. So not sure if Avast is the problem.

Lordbob75 said:

Try booting into safe mode. Start up command prompt (run as admin), and type this:

Code:

sfc /scannow

~Lordbob

Done, and it says it could not find any integrity violations.

Frostmourne said:

It could be heat - you have enough cooling in that case?

Hmm, not really sure. Besides the CPU heatsink, there's one fan in the rear side. My computer is on the ground though, but I've recently cleaned it up and there isn't that much dust. Might clean it again later thought.

DocBrown said:

It is a Retail Version of Ultimate, correct ? Not a Beta or RC1 build ? with an expiration date. at Start type > winver > select it > then click on it

Should be retail. It says version 6.1 build 7600.

I had a similar problem on my HP Pavillion running Vista.

The problem was a bad contact on the memory modules. All I had to do was very carefully remove the memory modules and reinsert them. Make sure you are grounded and that they seat properly.

lordbob75 said:

go into your bios, and look at temperatures. What are they?

~lordbob

cpu: 52-53
mb: 43-44