The other day I was going to ride my 1999 Gary Fisher Joshua F4 mountain bike and when I started riding it I could upshift with the RD,(would shift to the smaller gears) but I couldn`t downshift so I`m thinking maybe the shifter is messed up somehow. I don`t know if the shifter broke or cable broke. Is it maybe an easy fix? Here are some pictures of the rear shifter and RD. I just hope someone knows whats wrong and can help, thanks