Presuming you mean Avast 17.1.
Have similar problem but with PaintShopPro Photo X2 stopped working after free Avast upgrade. It’s there in Taskmgr.exe but no GUI.
Disabling all shields didn’t help. Works in Safe Mode and if I uninstall Avast.
Only thing that works is to go to Settings/Troubleshooting and unchecking “Enable Avast self-defense module”.
Not sure if it thinks there’s malware in the program but it doesn’t report it when I do a scan.