Unity 4.6.1 - "Opening File Failed: Access Denied"

Two weeks ago, my laptop’s hard drive crashed. Fortunately, all my Unity projects were backed up onto my external hard drive, so once I got a new solid state drive for my laptop, I re-installed Unity 4.6.1 (the version I’d had previously) along with all my other programs. Everything seemed fine, until I tried opening this one specific project.

First, it told me the project had been created in an older version of Unity and needed updating (I had
created in in 4.2.1, but I’d already upgraded it when I got 4.6.1 the first time round). I clicked “Update” or whatever, and a moment later I got a pop-up reading “Opening file failed. Opening file Assets/Prefabs/Block.prefab failed: Access is denied.” It says this for every single one of my prefabs, and for their .meta files.

I’ve checked my user permissions and I have full permissions for every single one of those files, so I have no idea why Windows would be denying Unity access to them. I’ve tried Googling the problem but I haven’t found anything. Is there any way this problem can be fixed or is my project gone forever?

I think it’s worth noting that my laptop was previously running Win8.1, but after the new hard drive was put in I installed Win7 instead, so maybe there’s some kind of compatibility issue going on.

Try to import your prefabs as aseets in new unity project. If you couldn’t achieve this, your files are probably corrupted.

I tried it and it said that I didn’t have permission to do so. Like I said, I’m pretty sure I already have full permissions for all the prefabs, but should I reset the permissions anyway?

EDIT: Turns out I don’t have permission to access the files after all. I’m gonna reset the permissions and see if it’ll work then.

EDIT 2: Turns out I don’t have permissions for any of my other assets either, nor do I have permissions for the meta files. So what does this mean?