I suggest the following:
A. Enable Windows Defender (WD) while Avast is not working. Normally with XP I do not recommend that you use WD, but you need some type of AV protection until Avast is working.
B. "Disable" (
not "delete") any unnecessary items in your Start Up to help speed things along.
C. When you installed Avast 5.0 but then went back to you last good configuration, this is where things may have gotten messed up with your prior version of Avast or another AV.
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Did you use a different AV on this machine? If so, what was it and how did you remove it? You need to use the vendor's uninstaller's tool and NOT a third-party uninstaller or cleanser.
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If you used another AV other than Avast, please post and let us know PRIOR to you doing an uninstall/clean install of Avast so we can properly give you the uninstaller tool for that AV.
D. Once you get your MS Updates done, then you will need to uninstall Avast and do a clean install:
1. Save a copy of newest version of Avast (5.0.677) for the version you need and save it to your HDD:
Free –
http://files.avast.com/iavs5x/setup_av_free_eng.exe2. Download the Avast Uninstall Utility, aswClear5.exe
http://www.avast.com/uninstall-utility and save it to your HDD (it has uninstall tools for both 4.0 and 5.0).
3. Disconnect from the Internet at this time.
4. Go to Control Panel and uninstall Avast through Add/Remove Programs if possible and reboot.
5. If Step 4 fails, boot into
Safe Mode (hit F8 repeatedly) and run the Avast Uninstall Tool.
You will need to uninstall BOTH 4.0 and 5.0 if you had both versions on your machine.6.
Reboot.
7. Install the newest version of Avast and
reboot.
8. Get Internet access and register your copy for Free:
Free –
http://www.avast.com/registration-free-antivirus.php9. Update the Avast definitions. Leave your setting at default for now.
E. You can uninstall or disable WD at this time. Instead I recommend using Malwarebytes’ Anti-Malware (MBAM), which you can download
free http://www.malwarebytes.org/ (the blue button) for an on-demand scanner.
F. Run Avast scans and do an MBAM scan (
update MBAM prior to scanning every time) to make sure you are malware-free at this time.
G. Keep your software up to date with
free Secunia Software Inspector
http://secunia.com/vulnerability_scanning/personal/, which will scan your software to make sure you have the latest security patches. This site gives you the vendor's direct download to make updating easy and many of us here scan our systems weekly since software changes so frequently.
Please let me know if you have any questions. Thank you.