Try using Revo Uninstaller. Even if it can't uninstall the app normally, it will force it to uninstall by wiping out all traces of its presence from the system.
Reboot the PC and start Revo Uninstaller again. Use the advanced module searching mode to look for PCMax, but it should be gone already.
If you believe this is a malware app, run a copy of Malwarebytes Anti-Malware.