external drive format problem!

I have been using my external drive divided into two partition
mac os format as a timemachine backup, and fat format for window.
and suddenly it started to fail the timemachine backup for no reasons...
so i decided to erase all the contents in external drive and do it all over from the start.
but the disk utility also fails to erase too. some error message pop up no matter what format i choose.
i tried to erase the partitions seperatively which also didn't work.
it this something to do with the external drive itself?
because it is having some problem with the removing process...
if i try to remove the external drive by moving the drive into the trashcan...
it simply dosen't do the work and makes the whole system freeze,
eventually i have to turn off my mbp by pressing the power button.
I am very confused because I always thought the last solution to external drive recognition problem was formating the drive clean but now i can't even do that.