I'm not sure how old your unit is but over time, the rubber parts in a VCR become cracked, glazed and begin to slip.
There is a rubber wheel about the diameter of a nickel that is called the pincher wheel and does exactly what its called.
It pinches or compresses the tape against a shiny metal spindle called a capstan. The capstan spindle is connected to a motor. The pincher wheel rests against the turning capstan with the tape in between the wheel and capstan.
The pincher wheel can become glazed and coated with a brown oxide that has worn off of the tape. This causes the tape to slip and it can spool out into the VCR.
There is another wheel called an idler tire. It lays flat and pivots between the sending reel and pickup reel. Its used during play, fast forward & rewind. This wheel too can become glazed and worn causing slipping. If your unit won't play, fast forward or rewind, most likely the idler tire is the culprit.
There are also belts that can also become glazed and worn. These belts are used along with motors in the tape load/eject mechanism and capstan drive. If the belts slip, the tape may not load or eject properly and the capstan might not be turning properly.
When I owned my repair shop, one solution was we to remove the belts and/or tires and apply a re-grip solution on the rubber with a cotton swab, while roughly rubbing the the entire rubber surface back & forth with the swab. The re-grip solution actually eats away the top surface of the rubber leaving the rubber surface course and causing it to grip better.
Another solution was to just replace all of the rubber tires and belts. These parts including the re-grip solution may be ordered through www.mcmelectronics.com
Please let me know if I may be of further assistance to you.