cut wire how can i fix it back?

"Wire" can mean the power cord or the cutting string...

If it's the power cord that's damaged do not attempt to repair it by temporary joining - just have a new cable put in - relatively easy to do yourself on some models if you're comfortable with simple hand tools. Depending where the damage is you might just shorten the existing cable or put an in-line connector (waterproof plug & socket) each side of the damage.

Good luck...

Peccavi
May 2009