My Drive C has a bad sector ? It is logical ? or Physical ?

Impossible to tell whether it is physical or logical. Determining that (and hopefully fixing the issue) is what checkdisk does. It will look at the sector and determine if it is physically damaged. If it is, it will mark that sector so that your computer will no longer attempt to use it and you will not get any ore corrupt files because it is trying to save them to that sector. If it is logical, it will fix the problem and make the sector usable again. If it can not, then it will again mark it has bad. You want to let the checkdisk run.

As for the Skpe, if you are getting a corrupt file error, you will need to reinstall the program once you have completed the checkdisk. Checkdisk only detects issues with file allotments and amrks sectors. It can not repair a corrupted file. The file will need to be reinstalled. As you have no easy way to know which file it is or to reinstall only one file, simply reinstall the whole program.