Dell D600 Won't Power Up?

I have a Dell Latitude D600. I noticed that over a period of use I'd snapped the wires inside the mains adaptor cable. When I noticed this, I moved the wire, as to pull it out and when I did so my laptop turned off (with no shut down or hibernate as it would if it were out of battery) and now refuses to switch back on.

Now, when I press the 'on' button I get the little 'power' light, but none of the other lights switch on (as usually happens upon start up). This light stays on for a few moments and then turns off - without starting up the machine at all; even the fan doesn't start.

I've got a new mains adaptor cable, but the laptop does this same thing whether it's plugged in or not, with or without the battery. I'm really not sure what it could be and I'd be grateful for anything anyone could give me.

Thanks