Here is what I am doing with all the hacked players I buy from China (I resell them after removing the hack).
1. Download...
http://mikelab.kiev.ua/PROGRAMS/ChkFlsh.zip
2. Run the program.
3. Check "As Physical Device"
4. Select the correct drive.
5. Check "Low Level Initialisation
6. Now go back up to the drive box and select the partition listing the hacked memory number.
7. Click start.
8. On the new menu that pops up remove all the partitions listed.
9. Create a new one on the number (1).
10. Slide the bar to whatever the correct memory size is (you need to find this out before hand).
11. Click ok.
12. Unplug device and replug when it asks.
13. Format device in windows.
The device should be showing the correct memory size now. Dump some files on and test it out.