If I understand correctly, you seem to have more than one “Avast” folder where should be only one? That’s an example of remnants, and such situation can also be found after going back to some system restore point.
I insist that filehippo.com has several old stable version of the Free edition, so you can download it anew.
Then download the removal utility for Avast (the link is in some post above), and reboot into Windows Safe Mode. Select one of the “Avast” folders (that should be the “correct” one) and run the removal utility for Avast 6.x. Then reboot, again into Windows Safe Mode. Repeat the removal utility procedure, but select the other folders each time, also with Avast 6. Now reboot a third time into Windows Safe Mode (and please don’t skip this reboots) and run the removal utility for Avast 5 (instead of Avast 6.x ). If you also had at any time Avast 4.x, then repeat the reboot and the removal again.
In theory, you shouldn’t have any relevant remnants of old folders for Avast after the cleaning. Relevant registry entries should have gone too. If you found anything related to Avast, try the removal tool again on the specific folder. Registry entries that might be left are not relevant (if you ran the removal utility for each and every edition and version of Avast you ever had in that old system.
Now that everything is clean, run the setup.exe for Avast Free (the one you downloaded from filehippo). Better yet, run the setup with “run as administrator” permissions. Reboot immediately after the installation.
After that last reboot, configure and test. Usu it for several days, and only update the definitions. Avoid FOR NOW updating the program itself.
By not updating the program, you should be able to test the system. This is not ideal, but in your case, it is better than having a “dirty” installation.
Register the new installation of Avast after several days of testing. Generally speaking, I do not recommend using older versions, but in your case, this seems to be the “best” of bad options, for now.
Please report back in any case. If you notice any BSOD, please try to save any type of memory dump (minidump, kernel dump, full dump).
If you have BSOD but no dumps are found, then follow the above instructions for creation of memory dumps so to upload it.
Only following the complete process and reporting feedback, Avast Team may be able to find the solution for your system.