Samsung Galaxy S3 Problem, can't mount /system?

So while I was away on the weekend my phone ran out of battery. I accidental turned it on and so I turned it off while it was on the Samsung logo, it seemed to had gotten stuck there. When I got home I plugged it into it's charger and for some reason it froze at the battery screen while it was loading, when it wasn't plugged in it froze on the Samsung Galaxy screen. I haven't rooted my phone at all, I merely use a launcher (I use Nova). I went into recovery mode and it actually had a red warning sign with saying it can't mount /system. I don't want to factory reset so any possible solutions would without ridding data would be of help. I have looked a bit online and people say formatting does nothing and to fix this requires all this knowledge of ROM and crap. I don't know why my phone all of a sudden has done this, I have done a battery pull and wiped cache partition but still nothing. Please help.

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