madde, Unless your player is a genuine 8GB Apple iPod Nano you may have a problem. These Chinese Nano Clones do not come in 8GB in fact they will only support a maximum of 2GB Nand Flash memory. What you have got is a hacked player, this is when the manufacturer adds a small capacity memory chip to the player and then programs it so that it reads as 4GB or 8GB. The fact that you can only use 10 songs indicates that your chip could in fact be as small as 128MB.
You will find that the files that cause your player to restart are corrupted, if you copy them back to your PC you will find they do not play. This is because they have been copied to memory that does not really exist.
If you look through the forum you will find many posts relating to hacked players.
Here are some posts that may explain.
http://www.mympxplayer.org/feedback-...rs-vt2828.html
http://www.mympxplayer.org/how-to-re...ck-vt2400.html
You can also open your player and check the serial number of the memory chip against this list of Samsung and Hynix chips
http://www.mympxplayer.org/samsung-a...rs-vt1692.html