SE3 wont complete launch - stops at: Midi Device Manager

I have never had a problem with my SE3 for years until now. When I launch it, it gets to: Intitilizing Midi Device Manager and stops. I get a CubaseSE3.exe has encountered a problem and needs to close window. It gives the option to send an error report (which I can’t because for some reason it wont connect) and a data error report:

Error signature

AppName: cubasese3.exe AppVer:3.0.2.643 ModName: cubasese3.exe
ModVer: 3.0.2.643 Offset: 002d54ea

The following files will be included in this error report:
C:\DOCUME~1\JANHAR~1\LOCALS~1\Temp\e2de_appcompat.txt

My OS is Windows XP.

Anyone any idea what is wrong here?
Cheers,
Jan

Thanks for your reply Steve.
I did do a system restore and I have now uninstalled and reinstalled the programme, but I still get the same problem.
I have been having some problems with computer performance, so I have been trying to sort that - AVG helped. I did download a programme to search for the latest drivers (as I thought this might be the reason why the computer wasn’t at optimum performance), but I removed the programme.

So, at the moment, I still need to work out what the problem is when innitializing the Midi Device.

I found the following at: http://www.cubase.net/phpbb2/viewtopic.php?p=963443

The germane question is did you delete or at least rename/move the Cubase prefs folder.
Also, since you had Cubase 4 running move its prefs folder too.

I have found similar on other posts - however I am not sure where to find this prefs folder so that I can delete it. Have been searching files on the computer, but nothing so far.

Update: I’ve sorted the problem.

Anyone facing similar issues should go to this knowledge base page for the solution:
https://www.steinberg.net/en/support/knowledgebase_new/show_details/kb_show/removing-the-preferences-of-the-sequencer/

Thanks for your post Steve.
Jan