I aint sure where the fuses are as I aint had to change a fuse for many years now but they are usually located behind a panel under the steering column and all the fuses are shown on the panel. To check them you just pull the one related to the stereo out and look through the top or side of the plastic cover and it's obvious to see if it's blown, the connection will no longer be a connection lol and they sometimes darken the plastic cover. It's simple but as suggested above, take it back and tell them it's not been working since you picked it up. A mate had an alarm fitted and ended up with an electrical fire, they tried saying the wiring loom was at fault and they hadn't touched it, but obviously to fit an alarm you have to wire it into the loom, so don't let them try to fob you off. if it was working but not since they had it, they are responsible for replacement.