I just got in a cousin's computer today to look at. It's a Dell Inspiron 1100 that wasn't powering up.

Here's what I've observed:

1) The AC to DC converter light comes on, meaning that I'm getting power as far as the transformer.

2) Removing the battery doesn't help

3) Absolutely no LEDs on the laptop come on, and no fans, etc. start.

Here's what I've tried:

1) We had a similar problem at work the other day, a lady brought in her Dell Inspiron that wasn't getting power from the DC port...the battery was powered however, and we had a few mintues of battery left to confirm that the laptop was working. We opened up the case to find that a copper connector that connects the port to the mobo was detached, we soldered it back on and it worked fine.
Thinking this could be similar, I opened up the case (and with almost 30 screws, that took a while) and saw that everything looked fine.

2) I've tried checking to make sure all the buttons work, and they do. There was nothing blocking the buttons when I opened up the case to look.

Does anyone know what's wrong and how to fix it? Or should I just tell him to buy a new laptop?

Thanks.

So you have reated all the things, like Ram; keyboard so forth (it sounds as though you know generally about all this)

You could also try reseating the CPU, but once this is done, you will then need to apply new thermal paste to fix the HeatSink again.

If you're really deetermined, you could remove the motherboard from the case fully, and benchtest it.

Even if the CPU isn't seated right, shouldn't I still be getting POST beeps and access to the BIOS?

No

If the CPU is seated incorrectly (or dry joint), you will not get any errors (displayed or emitted from the speaker)