Issue with Mail 2011 running in Win 7.

Starting acting up then couldn't reply, forward or send new messages.

Checked Microsoft site for help and attempted several of requested "fixes" including uninstall/reinstall, restore to previous time, internal self repair and others.

None worked and went as far as getting worse. At one point Pc wouldn't even restart and had to do that repair.

Now mail 2011 won't even open. Get message #0x800C0155.2- another program is currently using mail such as anti-virus.

What??? I don't have a second party anti-virus. Just Windows security ,Ccleaner, and Maleware bytes. Have always had these

I'm sure  during all this I have lost all email info by now.

Any help please.

Update- just tried to open again with same error message. This time when I closed message, a new bubble popped up saying "making a back-up copy of the database." ???????

Update 2 - think I fixed it for now. Had to revert to XP compatibility mode. If someone can tell me why I had to do this and how to fix it properly, it would be appreciated.

Thanks.