It is important to check the volume setting on your computer and make sure it is at 80%-90% of maximum level. Windows master volume does control what output you get from Soundcast products when played through your PC
Next, make sure that both the power light (green) and the link light (blue) are on and steady on both the transmitter and the receiver. If not, check the sliding channel switch on the back of each unit to make certain that both "ends" are on the same channel, 1, 2 or 3. Next make certain that the 3.5mm mini jack plug is inserted all the way in the socket on the transmitter and the RCA plugs are properly seated in the receiver module. It is also pretty important, though it sounds dumb, to check that you have connected the transmitter and the receiver to power and that the connectors and plugs are seated and fully inserted.