A Lot of the guys above have given some great advice, but i would like to refer to this.
Firstly, the server room being a mess, this can be corrected over time, might need some out of hours cabling work that you can just do as/when, get the important stuff done first.
But, Secondaly and MOST importantly, you are not a failure, you have a big job ahead of you, did you cause the problems? No, Are you trying to sort the problems?, Yes
This means you are not the failure, that would be your predecessor for not keeping their housework clean.
FAct is by the rough sound of it, this would be a hard job to walk into for anyone, regardles of experience, but being just out oeduction, it will feel like you are going to drown in the companies failings.
I would concentrate on putting a timeline in place (work on maybe a 12 month timeline) then Just sit down with your bosses, talk about the timeline, where you are at, at moment in terms of infrastructure / backups / software / requirements, and then how you are going to work through the problems over the coming months, this will give them something to be happy about, planning… and for yourself it means you can face the problems , in small byte-size chunks (pun intended)
But remember, when planning be realistic, if it is going to take 8 weeks to do a job, dont put 6 weeks becuase it looks better, put 10 weeks, allow for problems/contingency time, but then also if you finish in 8 week it looks good to bosses.
But, i will end with just 2 things.
Planning, Planning and Planning…
and more improtantly
you are not a failure, you are the one who has been left in the sh!t