Avast should be downloaded, and Avira stopped and uninstalled via "add/remove programs" before Avast is installed.
You cannot run two resident AV's together. Almost always.
The current Avast version is 5.0.396. It's a new version, and a few releases on from that new version, as many bugs have needed fixing.
Some users are still experiencing problems with the new version, and of these, some are (or seem) inexplicable.
I recommend the latest old version (I'm still running it, and in no hurry to upgrade.) It is 4.8.1368, and can be got at
Filehippo. Near the top right of that page, look at "old versions" and select the second. File Hippo is a reputable download site.
MBAM (choose the blue download- free version) should not be run in safe mode. Some of the low level drivers it uses require Windows to be running, to better access the features required to scan for and clean rootkits. It's on a par with SAS, better some days, the same on others, and following a quick scan, will produce a log. Everything should be ticked, and the "remove selected" button pressed. (This quarantines stuff.)
If you receive a prompt to reboot to finish removal, do so promptly.
As with any scanner, it should be updated before running, then it would in some cases be wise to disconnect the machine from the net. At least until after the reboot/rescan. (Yes, reboot it then rescan.)
If the same stuff - or similar - is still present, you're going to need more specialist help at a removal forum. Or a format and reinstall. Or you could keep attempting a fix using various demand scanners, or a BART CD.
Avira, DrWeb, and Kaspersky provide free downloads for the file needed to create and burn a BART CD, for which you will need a healthy computer with a disk burner.
Demand scanners that have a good rep at this sort of thing include DrWeb's Cureit, SAS, MBAM.
AndyManchester's site provides good links and brief info concerning various security tools. Worth a look.