At work I was very much frustrated with a machine of ours running Windows 8.1 and Avid MC 8.4.5. When MC was in the proces of starting, the program would hang at “Initializing media streams manager” for at least 5 minutes and when MC was finally started, opening a bin took several seconds. I tried to delete the database files as suggested by AVID – but with no result. Then my thinking was that the bandwidth to the ISIS server was limited – but that didn’t turn out to be true. Finally I found the solution: It turns out that the machine had ingested quite a lot of video during the last year so the local AMA XML file was extensive and was causing all the trouble with no benefits. So, I turned off AMA Managed Media and deleted everything in this folder:
C:\Users\Public\Documents\Avid Media Composer\AMA Management
as suggested in this thread.

Hope that trick can help you too!