Dell computer was working and i turned it on next

If your computer is under warranty, I'd suggest you contact either the Vendor where you bought it, or the Dell support site. Either should be able to acquire a new power supply and install it for you free of charge (if under warranty).

Some other thoughts though, before you do that. If there are no indicators that your power supply has died (smell burnt electronics, any weird buzzing sound prior to the computer not working, etceteras), then you might want to check the connections to the wall socket, the connection to the PSU itself, and even test the circuit breaker for your socket (some wall sockets have test / reset buttons that cut the power during surges).

-Jon