How to cure right arm numbness? Feeling numb when the arm is in "L" position like using the PC.

?ulnar. Your description suggests you may well be compressing ulnar nerve at elbow, but this could also represent an issue at the wrist. An EMG test could reveal location and severity. Contact your doctor and get opinion.
Carpel Tunnel ? Possibly carpel tunnel syndrome, or radiculopathy from cervical spine. Does turning your head affect the numbness ? What about bending your wrist all the way back ?