hard drive questions

So I have an original macbook air with a hard drive that is too corrupted to boot or repair but can be read and written to no problem (provided you boot from external media). If I wipe it and reinstall everything will work well for like a week and then it happens again. Thoughts?

Hdd's dead. Back it up and replace it.

many thanks. I was thinking the same thing but wasn't sure. Any chance there's another piece of hardware wrong? It's actually a friend's computer and I can saver her $$ by replacing the drive but if I'm not like 100% sure I just wanna send her to the apple store to figure it out.