My keyboard wont work right?

ive used this wired keyboard plenty of times but recently i got new pc and havent used old and i decided to plug it up today. When i plug it in the keyboards lights come on but then go off right after and it wont work. btw, its the kind of keyboard thats not usb its got the green round end. i will repeat I USED IT BEFORE ABOUT A MONTH AGO OR LESS