The first thing that you will require to check is whether the cable that you are using is working properly and if it's not damaged. Yet the charge will seize while the computer goes on stand by or sleep mode. This is something that you will normally. You must make sure that the computer that you are using doesn't get in such mode.
If these are not the actual source of the problem, it simply is resulting from the iPod being locked and for unlocking you should have it reset. Without unlocking it, you won't be able to have it charged through your computer. Please follow the below provided instructions to get the iPod reset: