A couple of months ago, my Mac Book Pro wouldn't start up - it would make it halfway through and then power down. I took it to the repair store, and they said the hard drive was broken, and they needed to replace it. (Interestingly, they were able to transfer everything in my Applications/ folder to the new hard drive, and that was actually 85% of my content.)
Now, my computer is having problems booting again. Sometimes it takes a long time, sometimes it doesn't finish booting at all. I was able to boot it into safe mode, and it seems to be working alright right now. What steps should I take now to deal with this problem and not make it any worse?