Brand new iphone 3gs won't start?

Got a iPhone 3gs for christmas (today), it is unresponsive so i figured i needed to charge it. It had been on charge for about half hour and still unresponsive, so i plugged it in to my laptop to see if the laptop would recognise it but it hasn't even told me anythings plugged in. I have put my sim in it and have tried turning it on and also tried holding the home and power button together for like thirty seconds cause that used to make my ipod reboot.having no luck, what do you suggest? Should i leave it on charge all day and come back to it tonight or does it sound broken? I don't think its BRAND new, mum got it off a friend, but its in all the packaging and other than the key to get sim out missing (i had to use a paperclip) its all there and in mint condition.

Try leave it to charge for about a half day or so, and if it still doesn't work, it may be because the battery is faulty, so then take it to your nearest phone shop.