What softsynth said^^
you could try something in standalone as well as vsti. Also, try a midi cable??
In Reaper, set up a midi track with vsti on it and your kb selected as the device, if a midi signal is getting through you should see a red line appear each time you press a key (despite no sound). If no midi signal then it is likely a problem en route from your keys to reaper.
Hmm, Reaper setup ok?
try different cables, wiggle the connections slightly
google
good luck
