Ipod wont turn on

Hello, I saw ur advice of holding the center button and the menu button down 4 30 secs but it did not work on mine what shall i do.

it was working fine yesterday but the it kept on comming up with the apple screen and then it switched off then i came up again with the apple screen then it switched off again it just kept on happening and i put it on charge becaus i thought it was the battery but it still didn't work and when i plug it in my computer it says device not found and it dosen't let me restore it on itunes at all not even the icon of my ipod comes on

please can you help me

Thanks ever so much