Laptop not booting : queries about boot process

I had a really old Dell Latitude C500 Laptop lying around, and for some reason I decided to dismantle it completely and put it back together (following this manual).

When I reassembled and tried to power it on, the monitor remained blank (no response whatsoever), and some LEDs tued on (details below). Everything switched off after about 5-10 seconds.

I'd like to know some details about a typical laptop boot process so that I can debug this according to the following symptoms.

1. Power indicator LED tus on, and remains on even when the laptop tus off. (Normal)
2. Caps lock and num lock LEDs light up and scroll lock flashes (Normal).
3. When I insert the CD drive and HDD, they both whirr normally. (2 and 3 cut out after 5-10 seconds).
4. On attaching an exteal monitor, there is still no response.
5. On removing the microprocessor, lights still come on but HDD and CD drives are silent.

I've tried resetting the laptop by holding down the power button, removing battery, etc. I've also tried removing CMOS battery, RAM, all exteal things (PCI, CardBus, HDD, CD drive), but the lights still shut off after 5-10 seconds.

Fn + Power button doesn't work. Inserting a bootable CD doesn't work. No beeps generated in the whole process. I've read somewhere that there is a way to coect a speaker to the motherboard to read beeps corresponding to error codes, but I can't figure out how.

According to this link, POST checks the secondary storage devices and then the BIOS looks at CMOS for Boot Order.

But several other sources mention that the monitor comes on during POST (ie, it should display the DELL logo and stuff). So if POST isn't reached, then how does the HDD spin?

Is the HDD and CD drive spiing just a self power up routine? If so, why does it not happen when the microprocessor is discoected?

Overall, I'm pretty confused with the boot process. Is the BIOS corrupt? Is the CMOS chip damaged? Or something else?