Can't install antivirus program

[nicwatts]

Hi. Am very new to this...so please forgive any mistakes I will make.

I have been having problems with my pc ever since I installed xp sp2. Recently I tried to access www.avast.com to download an antivirus program someone told me was good because I had removed spybot search & destroy, lavasoft adware, att/yahoo antivirus and just wanted one good program.

Problem was as soon as i typed in address in browser and hit go...browser immediately closes. I tried several times. Also, whenever I type the word "virus" into a search engine, my browser closes. I am currently on my kids pc to try & figure out what to do next.

It looks like I need to download hijack this first...but am afraid I won't be able to do on the problem computer. If I don't hear back right away...I will try to get that done at least. I have many more issues with said computer, but this is where I need to start.

Any advice will be GREATLY appreciated.

[gerbil]

It's Saturday, and I'm going out; this is rushed, but should help [playing a bit blind, here...], do these things in this order:
==Download this temp file cleaner from http://www.atribune.org/ccount/click.php?id=1 --click in the download window to run it, and when ATF Cleaner opens go Select all, and then Empty Selected.
Next click Firefox [if you have that browser..] at the top, Select All again, and Empty Selected again. Follow that procedure also if you have Opera.
Close ATF.
==download HostsXpert from http://www.funkytoad.com/content/view/13/31/
-click the top button Make Writable if it is available
-click Restore MS Hosts File button.
==Please use IE to do an online scan at panda:- http://www.pandasoftware.com/products/activescan?
-select a link to the scan... free online virus scan...., enter a valid? email and follow through, choosing My Computer for a full system scan.
Post the log it produces here.
==GET AVG antispyware 7.5 here.. http://free.grisoft.com/doc/5390/lng/us/tpl/v5
or here.. http://free.grisoft.com/freeweb.php/doc/5390/lng/us/tpl/v5#avg-anti-spyware-free
-Install it and UPDATE it.
Start AVG a-s 7.5;
-under Scanner/ Settings please change the default action from Recommended Actions to QUARANTINE, and run the complete system scan.
-press Apply all Actions and Save the log file. Post the log file.
==download hijackthis: http://www.majorgeeks.com/download5554.html
-copy it to a new FOLDER placed either alongside your program files or on your desktop and then... rename hijackthis .exe to imabunny.exe
-in that folder start HijackThis by dclicking the .exe; now close ALL other applications and any open windows including the explorer window containing HijackThis.
-click the Scan and Save a Logfile button. Post the log here.
Should keep you quiet for a while.

[gerbil]

Just a note... It is the hosts file which is blocking your browser from some sites. If you wish to clear your hosts file manually [C:\Windows\system32\drivers\etc\hosts] you may not be able to save the changed/corrected file. This is because some security applications, possibly also various malware, will lock your Hosts file ...
Go Start, run, type cmd -press Enter. Paste this line into the window at the prompt, press Enter, close the window and try to save the file again.
attrib -r -h -s %SystemRoot%\system32\drivers\etc\HOSTS
..but Hoster will do all this for you if you wish.