Re: Lightsaber and Workbenches not working!
There's two cases where you cannot use your lightsaber. One is when you're walking near friendlies in non combat areas, and the other is after encountering Jaro Tapal when first trying to access the tomb at Dathomir. That is because during that encounter with Master Tapal, your lightsaber gets broken. It's the main reason you need to go to IIlum.
As for the saber or benches not working after it's repaired, I've never had that happen in 3 play throughs, nor have I seen or heard of anyone else have it happen. I suggest maybe running a game file integrity check.
It is possible your save got corrupted though, and as far as I know, since there's no backup saves, there's no way other than starting a new play through to get around that.