wierd system default

A couple weeks ago one of my friends in school asked me about his system not working. Everything was hooked up fine and all fuses were fine. The only thing that wouldnt turn on was the amp for his subs. I checked the fuse right next to the battery and it looked perfect. He ended up just replacing the fuse with a new one and it worked. This happened again to another friend today and i told him to replace the fuse and he did and it worked. All the fuses were perfect. I wanted to know why this is and what causes the fuse to become faulty. Thankyou03 F150 on 24's

HU:Pioneer DVD5700

Frt:MC57

Subs:(12)S12L7

Amps:(3)KX2500.1's, MC-2004

Could be many things, including corrosion or oxidation on the fuse or the fuse holder.  Did you try cleaning the contacts on the old fuse?  Oh, and are you certain the old fuse is good?  Did you check it with an ohmmeter?  Also sometimes when some amps shut down or go into protect for some reason it needs to be reset by removing constant power, which you did by pulling the old fuse.Support the12volt.com

no i did not check that. What would all of a sudden make a good fuse turn into a bad one or not have an ohm reading?03 F150 on 24's

HU:Pioneer DVD5700

Frt:MC57

Subs:(12)S12L7

Amps:(3)KX2500.1's, MC-2004

dyohn was trying to tell you that it was possible the fuse was blown but didnt look that way.  sometimes the fuse can blow at the end of the "glass tube" and when you look through the glass all looks fine.  with an ohmmeter you could meter the resistance across the fuse to confirm or disconfirm.MECP certified, 5yrs experience, you probably otta listen bitch!!