F2 fuse burn (2 replies)

Hi all,
i just finished mouting a prusa i3 3D printer. everything was working well (all motor move in the correct direction) untill I want to heat the hotend and the heatbed to began my first print. The hotend was hot but not the heatbed when the F2 component (a fuse according to the wiki) start smoking.
the power supply is 12v 33A.

what did you think make the fuse burn ?
did you think the ramps is still working (if i replace the fuse) ?

should i cool the ramps with a fan ?

thanks for any help