I was running Tails from a USB flash drive until I shut it down one day and it stopped booting. Afterwards, I booted into Windows to fix it, and the system didn't even seemed to recognize it. So I opened my partition manager to check on it, and everything looked normal. And it wasn't formatted in ext3 or anything, so it should've showed up in Explorer.
So far, I have tried using LiLi USB Creator and UNetBootIn; formatting into FAT32, NTFS, and FAT16; deleting all partitions; and initializing to GPT.
I have tested with another live OS (Tinycore) on my main computer and another one with similar results.
When I try to boot from the drive, I select it from the BIOS boot menu after pressing F12.
What happens after telling it to boot is I get a screen with white text on black, and it says "Intel UNDI ... For Realtek ... PCI-E Ethernet Controller ... PXE-E61: Media test failure, check cable / PXE-M0F: Exiting PXE ROM...." and it repeats the message infinitely. It looks like it's trying to boot over LAN instead of USB.