|Can you access Task Manager by pressing Ctrl+Shift+Esc? If so, look in the Process tab for explorer.exe If it's there, end that process. On the Application tab, click New Task and type in explorer.exe Explorer (not confused with Internet Explorer) is the desktop shell. With that process started, your Taskbar and Desktop icons should appear like normal.|
Whenever you detect malware, you should run a full system scan. If you still can't get regular boot to work right, boot in Safe Mode and perform your scan. If you don't have the latest program update and malware definitions, boot in Safe Mode w/ Networking instead, then do a full scan.
Since no program is perfect, I recommend you download and install Malwarebytes Free (http://www.malwarebytes.org/products/malwarebytes_free) and use it regularly along with Avira. The free version of Malwarebytes is an on-demand scanner, so it only scans when you tell it to and it won't conflict with your real-time Avira.
Apologies if I don't respond to your reply immediately. I don't check this site daily, but you're welcome to PM me as a reminder.