I had numbness in my hands when I first started riding. Found out a lot of it was related to posture and fit.
Here's some tips from Livestrong if you haven't considered posture or fit yet.
If all else fails try a pro bike fit at a shop, nothing worse than not riding cause your bike doesn't feel right
Improper Posture
If you have poor upper body posture, you can experience wrist pain from your mountain bike handlebars. Make sure you're not trying to support your body with your wrists and hands on the handlebars. If you find you're putting significant pressure on your wrists, roll your shoulders back and bend your elbows slightly, which will provide you with a better ability to absorb shocks. In addition, try tilting your bike's saddle back a small amount, since if you've positioned the saddle too far forward, you'll tend to slide forward and place too much weight on your wrists.
Improper Fit
If your wrist pain continues even though you've made adjustments to your posture, you may have a mountain bike that doesn't fit you properly. To find out, measure the distance between the forward tip of your saddle and the center of the handlebars. That distance should equal the distance between the end of your middle finger and the outside corner of your elbow. If it's too long, you're probably overreaching and may be putting excess pressure on your wrists, while if it's too short you may be placing your wrists in an awkward position. See a professional bike adjuster if necessary to get it right.
