WINDOWS XP KEEPS LOGGING ME OFF FOLLOWING AVAST SCAN

I recently downloaded avast free antivirus to my partners laptop which uses windows xp proffessional edition.

Following a quick scan (which took around 5 hours) I closed the machine down

Trying to start it again the following day I find it is constantly logging me off.

When the username and password are entered and the ok button pressed a screen opens with the message

‘Your personal details are being loaded’ and then promptly dumps me back to the login screen, it’s like being caught in a loop.

I would be grateful for any ideas. ???

did you remove any previous installed AV before you installed avast ?

Can you start in safe mode ?