I posted this on the Avast forum but they had their tech guy on vacation and they guided me here so here's my original post from Avast forums:
Hi! After Windows 10 came out I installed it on my desktop, but noticed my graphics card was not supported so I went to Windows 10 setting and selected to return back to Windows 7. After what seemed to be completed revert my computer got stuck on infinite reboot loop. I can see all my files on the hard drive using Try Ubuntu usb-stick so the HDD isn't corrupt. After trying to start it in all ways possible(nothing worked) I saw in the safe mode boot log that the file my system hangs on is aswrvrt.sys. I have no clue how to continue from this. I have a laptop from which I can download programs to run on the desktop if needed. Thanks for your help!
I try my best to answer all the questions you have. I might have forgotten to mention someting so please ask freely! Thanks!