More to the point, a system restore does exactly what it says on the tin, restores the "SYSTEM"... not applications! it wouldn't effect excell at all!
And yes, 95% of recommendations for a system restore on here are drastic.
The OP hasn't mentioned what version of Excel they are running so it's a bit hard to be precise, but the chances are the toolbar file has become corrupt, if that's the case all that's need is delete the toolbar config file and excel will create a new one next time it's opened, it should fix the problem but any changes made to the toolbars will be lost.