"the System Cannot Find The File Specified Usb Format" Usb Flash Drive?

I'll warn up front that this is a duplicate of another forum entry, but although that other entry is now closed, the solution was never postedI recently turned my 8GB Sandisk usb into bootable usb in order to run chrome os,everything was ok untill i needed my usb to transfer some files so when i plugged it in while running windows 7 a box popped up to format it i clicked ok,then i noticed the usb from 8 GB showed up as 1 GB in my computer.I opened disk management and saw that it was cut into many partitions, i deleted some of them so i would expand it in one partition,at that point my trouble began,the expand option was greyed out,i tried diskpart and delete the partitions there.After that the drive lost its assign letter and showed up as one partition in disk management but in my computer it was invisible,i tried other guides that use diskpart.when i try to format or assign letter from disk management i get this message "the system cannot find the file specified usb format".