I just bought a 1997 mazda 626,automatic transmission, 4 cilinder, it has about 120,000 miles. When i turn it on it shifts perfect into all gears, then it will completely stop moving in any position including reverse, so i turn it off then back and on and it shifts perfectly, then after a while it will do the same thing, i dont know if its soemthing electrical or what, any help would be greatly apreciated.