Q: Mini-display port to hdmi cable not working consistently

I have a MacBook Pro (15-inch, Early 2011) 2GHz Intel Core i7, 4GB, Intel/ATI combo video - Yosemite 10.10.2. I purchased the monoprice 15" mini-display port to hdmi cable and it worked perfectly for about 1 month or 2. Now when i plug in the cable, the MBP doesn't detect that I have a second display connected at all. I assumed the cable died so I tested it on my iMac. The cable worked. Also when I try my Monoprice 15" mini-displayport to VGA cable, that works on my MacBook Pro. I can't figure out what is causing my MacBook Pro to "forget" how to detect this cable. Anyone out there experiencing the same? I tried PRAM reset to no avail. Any suggestions would be great.