Avast v.7 stopping Avast Pro Antivirus -BlueScreen

[kmcd]

I am using Avast Internet Security v.7, and wanted to try the free version of Avast Pro Antivirus.  I downloaded it, but when I tried to install it the original Avast program blocked it.  It threw up a little message in the corner of the screen, but before I could read it and click the option it gave, I got a BSOD.  I tried three times and finally gave up in fear! If I turn off Avast will it allow the Pro to work?  I am kinda scared to try it, not being very computer savvy..I have a Google redirect virus I am trying to get rid of, hoping the Pro version might help. 

[Lisandro]

I am using Avast Internet Security v.7, and wanted to try the free version of Avast Pro Antivirus.

You have to uninstall AIS first. Indeed I suggest an installation from scratch.

I have a Google redirect virus I am trying to get rid of, hoping the Pro version might help. 

Well... Don't get a false impression. The cleaning capabilities of the Pro version aren't higher than the free in theory. Only the protection is higher.
I suggest:

1. Clean your temporary files.
2. Schedule a boot time scanning with avast with archive scanning turned on. If avast does not detect it, you can try DrWeb CureIT! instead.
3. Use Comodo Cleaning Essentials (CCE), or MBAM, or SUPERantispyware to scan for spywares and trojans. If any infection is detected, it is better and safer to send the infected file(s) to quarantine (Chest), rather than simply deleting them.
4. Test your machine with anti-rootkit applications. I suggest avast! antirootkit or Trend Micro RootkitBuster.
5. Read these instructions and provide more info with the logs generated. But, please, do NOT post there, open a NEW thread for your specific problem and help us to help you.
6. Clean your Hosts file (replacing it) with HostsMan tool.
7. Disable System Restore and then reenable it again.
8. Immunize your system with SpywareBlaster.
9. Check if you have insecure applications with Secunia Software Inspector.

If the infection avoids booting the computer, take a look here http://forum.avast.com/index.php?topic=79107.0