Avast on windows 7.It wont install. Need advice.

[Denv12]

I bought a new computer 6 months ago with Windows 7 home premium.It already had Nortons internet security 2012 on it(for a trial period),I put Avast free anti virus as well and ran them at different times,never at the same time.I added avg standalone linkscanner to the pc.It worked a treat.

When it came time to renew I chose to uninstall nortons and then avast.I used zonealarm since.Today,I uninstalled zonealarm completely.Then I reinstalled nortons(which I did) and avg linkscanner(done) and tried avast.It didnt install.I kept getting that reboot message then it still wouldnt install.

I really dont know what to do.

I even tried to download the avast removal tool to see if that might help.It wouldnt install that.

My pc has now got nortons and avg linkscanner.

Can you please tell me why I've had problems installing avast? Should I just leave the pc with nortons/avg linkscanner?

Thank you.

[Asyn]

First, be sure to get rid of all remnants of your prior installed AVs.
-> http://singularlabs.com/uninstallers/security-software/

Then:
1. Download avast! Free Antivirus: http://files.avast.com/iavs5x/avast_free_antivirus_setup.exe
2. Follow instructions: http://www.avast.com/uninstall-utility (Run this tool for all prior installed avast! versions..!!)
3. Reinstall avast! with the downloaded installer from point 1.
4. Reboot.