Default halfway rooted and need to stock

I bought my prime about a year ago and immediately rooted it but kept the stock rom on it. At some point it lost it's root, I guess from an OTA. Apps like titanium backup tell me they can't find root.

But I am also not unrooted either. Something is screwed up and I can't OTA update anymore.

Can someone please point me in the direction of getting my Prime reset? I like the stock software and only want root for titanium backup and es file exlorer.

I am currently on ICS and have done the Asus unlock.

Sent from my Transformer Prime TF201 using xda premium