Dell Inspiron 1720 Power up problems

My brother-in-law's Inspiron 1720 won't power up with the onboard power button (no lights, activity at-all). However it will boot into the media centre using the "home" button next to the power button. I've removed and re-placed the keyboard (which also hosts the power buttons) and no difference.

If I remove the keyboard and plug in the power then the machine boots into the POST complaining about lack of keyboard (funnily!) and then if I put the keyboard back in and cancel POST, it boots to Vista and I can use it. However, after the next power down I have the same problem as the power button doesn't work.

Given that the keyboard works, and I can boot into the media centre, could this just be a keyboard power button problem, and replacing the keyboard would fix it?

Thought I'd ask before purchasing a replacement keyboard....

Thanks

Dave