Hi
What format was used on the usb drive?
(Fat32, NTFS, MAC or one of linux EXT2..)
what operating system is on your PC ?
I assume some sort of Windows.
At first not clear if pictures taken using a RAW picture format or the USB drive can not be read
usual cause of needing re format is pulling drive out before writing has finished
have you tried chkdsk yet and had an error?
(chkdsk works for FAT and NTFS and can make apparently unreadable disks readable providing no physical damage has occured)
Quick format in Windows PC does not destroy data but is only used as last resort before using unformat options in data recovery software
Quickest and safest option to get person who gave you the pictures to give you another copy
regards
Mike Barnes