Black screen with cursor at startup and before "Welcome" screen

Installed AV 2015 on 3 machines and mistakenly paid for it. 2 running i3, the 3rd running an Athlon x2 Brisbane. All had black screens, all had extended boot times (from 3 mins to 6 mins) and all lost mouse control for a few seconds after finally logging in. Bit-defender tried to help but essentially only told me to do what I had already done. Namely, cut boot programmes, cut various services blah blah. Boot times did not change so I removed Bit-defender and put back MS Security Essentials. Bingo, boot times now back to normal (anything under 1.5 minutes is my benchmark). Bit-defender may be the best AV but then so is not switching on and logging on. Leads me to wonder about the various reviews and the integrity of the reviewers. First time I've paid for an AV since Norton was taken over by Symantec in 1990 when the price went up, bloat appeared and the quality went down.