How about booting Swapmagic without any USB devices inserted? If it does boot, it means that your USB device is probably incompatible as the USB drivers used by Swapmagic are quite unreliable with certain USB devices.
Originally Posted by alextilman
If Swapmagic cannot boot at all, it could be either a problem with your console's laser or your Swapmagic disc is faulty.
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit