Blue screen problem, with Windows XP

[EoinF]

Hi, the title sums it up, but I'll explain.
Yesterday, my family got a USB Mobile Broadband Dongle (3 is the network) for our computer. We'd never had broadband before on this computer. Anyway...
Today, I was helping my younger brother make a Facebook profile when a message popped up saying something like 'Windows has applied an update, and requires restarting the computer in order for the update to take effect'. I chose to restart later.
A few minutes later we'd finished, and the same message popped up once again. Since we'd finished, I said 'Fine, just restart it now..'.
When I did, I got a message saying something like 'Windows did not shut down successfully.' (I can't actually remember what it said, but was given several options of starting Windows). I chose 'Start Windows Normally'.
I was then greeted by a blue screen reading-

A problem has been detected and Windows has been shut down to prevent damage to your computer.
If this is the first time you've seen this stop error screen, restart your computer. If this screen appears again, follow these steps:
Check to be sure you have adequate disk space. If a driver is identified in the stop message, disable the driver or check with the manufacturer for driver updates. Try changing video adapters.
Check with your hardware vendor for any BIOS updates. Disable BIOS memory options such as caching or shadowing.
If you need to use Safe Mode to remove or disable components, restart your computer, press F8 to select Advanced Startup Options, and then select Safe Mode.
Technical Information:
*** STOP: 0x0000007E (0xC0000005, 0x8053616C, 0xF7A31508, 0xF7A31204)

I'd used Google to look around for a solution, and was lead to a page on this site. I can't currently find any disk that came with the computer, but upon accessing the Recovery Console... C:\WINDOWS>chkdsk /r... The bold text being what I typed. I waited for that to finish and got a message along the lines of 'One or more errors has been found and corrected', amongst numerous values for volume, or something.
However, still nothing. When I restart, the same Blue Screen is there. My friend recommended uninstalling the Broadband Modem, but I'm not sure how to do that from the Recovery Console (as I can't access regular Windows XP). I really need serious help with this, please- sorry if I shouldn't have posted this.
Also, though a format would be a drastic step (in that everything is deleted), would I be able to start again with my PC, as the day I first started it up? I just need to make it work normally, really, but preferably without having to buy anything extra or something- however, I wouldn't rule that out. Please, could somebody help me fix it?
EDIT: I'm so sorry, I noticed the BSOD section just now.. On my mobile screen earlier I hadn't noticed it, so... Sorry for the waste of bandwidth, guys.

 

[Route44]

Can you boot into Safe Mode?

 

[EoinF]

I managed to make a bit of progress after a bit more research- I pressed F8 during startup, and was given different options- Safe Mode was also there. When I'd chosen Safe Mode before (without having pressed F8) it lead to another Blue Screen. But pressing F8 and choosing Safe Mode leads me to two choices- Windows XP Home Premium Edition, and Windows XP Recovery Console. I chose the former, and got a Blue Screen. I restarted, and chose Recovery Console, and following instructions I'd seen on a thread here, I typed in "chkdsk /r". I let that run, and it said a few things about volume, then that an error was found and fixed. However, still got the Blue Screen. So, I looked around and asked a few more people, and various people and pages mention an Antivirus...
Wait, I forgot to mention (damn, sorry)- as soon as I was able to use the internet, I downloaded Avast Antivirus and installed it, then downloaded and installed Mozilla FireFox. The sites and people I was talking about mentioned the installation of an Antivirus leading to a Blue Screen. Another guy and I have drawn the conclusion that Avast is what lead to it, and so I need to uninstall it. However, since I can't access regular Windows even through Safe Mode, I need to do it through the Recovery Console. This is where I now need help- I need to know how to find the file path, and, to an equally important extent, what I type to uninstall it. Sorry if I'm being a bit vague, but I'd like to know how serious a problem this is, and if you can help me solve it it'd be most appreciated. (for one thing, my mother wont murder me- she has very little understanding of things like this, and so assumes anything wrong with a computer is a virus or something).

 

[LookinAround]

I just got home... quickly skimmed your thread.. and a few comments before off to bed

1) Do you already have a copy of all your personal files/folders on backup? If not, you might start with [post=766270]How to recover your folders/files when Windows won’t boot[/post] to get a copy

2) If you think malware might be involved do be careful about scanning the backup when re-connecting the backup drive to a clean computer (more about that later)

3) I think the next best step to try and unwind this problem is probably trying to do a system restore to see if a system restore can be applied and you might have a restore point prior to when the problem began

As to your question, a full reformat and reinstall should get you back to working computer (assuming you don't have any hardware failure.. tho from your description doesn't sound like hardware is the problem)

in any case... off to bed now... ZZZZZZZZzzzzzzzzzzzzzzzzzzzzzzzz