Serial interfaces are no coming up on Cisco router 2501?

[Mian]

Hi
Im trying to to set up cisco routers (2500 series) for CCNA studies but due to some reasons the serial interface s0/s1 are not coming up.

Before assigning ip address ,clockrate at DCE interface and no shutdown commands the show interface command says the following:
Serial0 is administratively down, line protocol is down
Hardware is HD64570......

And after ip address,clockrate,no shutdown command ,
show interface reads like
Serial0 is down, line protocol is down........

show controller command does not show the type (DTE or DCE) interface.(as it shows in simulator)
I changed the cables changed the routers (I have four) , reload the routers, even set back every thing to default factory default settings but nothing works.

One thing I noticed that the led were off on all serial interfaces on all four routers but ethernet leds were flickering.
Your professional advice/help would be highly appericiated.

Thanks

(I managed to configure the routers , completely in the simulator but not with real hardware)

[RouterPouter]

Mian,

I've only done virtual lab work, but from what I remember reading, if you've got the correct working cable plugged in (but perhaps other settings incorrect), you should at least see " Serial0 is *UP*, line protocol is down." I'm hoping someone else can jump in here and set us both straight. And this is obvious I'm sure, but your DTE/DCE cable is labeled at both ends right? And the right ends are in the right serial ports?

Sorry, this may be a big bag of obvious, but I'm trying to help..

Brian