Which Dell Model?
Very slim chance a 3 year old model will be available in regular stores, and they wont sell only the receiver.
Try ebay to find a replacement receiver.
Or find an electronics repair shop and ask them to check.
P.S. Whats with the thread title?
"Dell wireless keyboard receiver not working" would be apt.
"Help!!!!!!" is if your computer sprouted legs like a Transformer and started chasing you..