If you've formatted your player and it is now 1GB, then chances are that your player only has a 1GB memory chip installed inside the player.
The best way to check is to open the player and post details of the memory chip. Then we can search on the chipset numbers to find what size memory chip it is.
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hacked players are purposely hacked to show 4GB to fool you and the computer into believing it's 4GB. However, if you format it you can remove the hack and show it's true memory size. In your case, this is what seems to have happened. But to confirm, just open your player and post the memory chip numbers.