It isn't another instance you have to watch out for, it is another application that uses the same instance as ITA.  It sounds like your database is corrupt, so you'll need to create a new database.  Sadly, that means another reinstall of SQL and ITA.
All was working fine. Dedicated VM server just for ITA. Running Ok for 8 weeks. Then just 3 days ago....boom! ITA does not display Software Updates any more. It whinges about increasing the timeout, but that doesn't help. In fact changing the timeout to 180 (from 60) and it still times out at 60!! Go figure.   QUESTION: If I un-install and re-install ITA, will it lose all the discovery data that has been put in??   Thx, John Bradshaw
ITA 8.8 Software Updates blank