Not a problem you can use "AVG" and malwarebytes simultaneously.
I sujjest, its better to go for good Antivirus like "Avast" or "Bitdefender" (freeversion).
Did you check the temporary files in C:\ Drive of your machine. Cuz., computer may also freeze if the there are huge amount of temporary files.
Use Ccleaner and free all the temporary files, and then fix all the registry files using the same application.