Besides what vojtech asked for.
Can you either post the exact error message or a screen shot of it ?
Is there anything more in the windows event log, either application of system logs ?
Have (or did) you have another AV installed in this system, if so what was it and how did you get rid of it ?
Task Manager should show ashMaiSv.exe as running is it ?
You can also check the Internet Mail provider details, the Last scanned: and scanned total: should indicate if it is working and scanning. There should also be an icon in the system tray only when it is actively connected/scanning email when completed it goes.