It wasn't like this before. Somehow, if I leave my USB plugged in, my Mac doesn't boot. Instead it gets stuck at the Apple logo with a very slow progress bar. When the bar finishes, it just waits. I tried resetting the PRAM but nothing changed. I also tried booting into Safe Mode, but it wouldn't boot. I did boot into Recovery Mode (cmd + r), and was able to repair the disk, but it said everything was fine. But I still can't boot my Mac. What should i do?
PS: I dont know why, but there is a Disk named Mac OS X Base System in Recovery Disk Utility, which I only see when I can't boot my Mac. I also can't eject this.