External Harddrives.
My bro and I bought a 500gig off of
http://newegg.com for less than $90.
I suggest looking on there or posting in Tech Talk for help finding a 500gig-1 terabyte external hard drive.
Once you have one, password protect it and then back up all the data you want to keep.
Unfortunately this won't return your lost pictures, but it will keep them safe from your dad(unless he's a hacker).
If you have (or rather when you have) any really,
really important files, you could buy a 32gig (or possibly 64gig by now) flash drive (they're about 3inches long) and then hide it in a special box or something.
Thankfully I and my bro are the 'Techies' in our house (and pretty much neighborhood) so our father couldn't do that.
Are you on a network with other computers, like your sibs/mother/father?
If you are, then your dad could've moved the files to another computer while he reformatted it.
Nevertheless, he should've asked you. It was wrong of him to do that. Unfortunately we can't change it.