usb live stick, lost bootability and accessibility

i made bootable usb stick using winsetupfromusb.exe, content multiple useful tools, such hirenbcd, ubcd, antivirus, tails... and many *.iso.
few days ago, i was messing around ubcd tools and ended ruined my boot usb repair tool.
all data and iso are intact, all subfolder are still browse able using "active disk editor" and winhex.

disk management console (win):
shows "online", "k" drive, healthy (active, primary partition), RAW

when i plug in computer to boot up :
it boot into grub4dos (instead of landing at menu for me to select which iso to boot up with ), it just landed in
grub>
**because "invalid first FAT entry (0=1001)!" *** it can't locate menu.1st file.


when i type in some grub commands:

grub> boot
error 8: kernel must be loaded before booting

grub> configfile
warning! invalid first FAT entry (0=1001)!
error 15: file not found

grub> geometry
drive 0x80 (LBA): C/H/S=1906/255/63, sector count/size=30619890/512
partition num: 0, active, Warning! invalid first FAT entry (=0x1001)!
filesystem type is fat, partition type 0x0c



from all the info that i provided, anybody can teach me way to solve the problem or explain the issue

thx
andrew

"Messing around" covers a multitude of unknown activities.
Wipe it clean and start again,without messing around.

since MBR are all standard, is there no way to reconstruct it ? or maybe just the location of first file that is wrong.. is there no way to just manually edit it and get it fix ?

just format and redo, then there is no more fun isn't it ? don't know, just thinking since my data are all good, .... should be just "pointer" are pointed to the wrong place...