If the fuse was blown, it would not power up at all.
First, try a factory reset - hold the A (or Clean) button in while turning on the power and hold it for 5-8 seconds.
If this doesn't work, you shoudl be able to bring the amp back to where you bought it for exchange - most stores have a 30 day return policy. If not, you will need to bring it to a Line 6 Service Center for evaluation.
+1 to fflbrgst. But, to answer your question about how to access the fuse; you may need to carefully use a small "flathead" screwdriver for leverage to open that panel (it pops out). The power circuit fuse is in there.