Tt61 power button doesn't respond

[caveat]

I recently completed several upgrades to my t61. Before the upgrades, the power button worked. Since completing them, everything is working well except that the power button has stopped responding under any condition. The only way I can turn the machine on is by removing the battery and AC plug, then plugging in the AC adapter.

Upgrades completed:
1. Flashed Middleton BIOS
2. Replaced HDD with SSD
3. Installed Windows 8
4. Replaced wifi card with Intel 4965AGN
5. Replaced battery

Fixes attempted:
1. Replaced keyboard (no change)

Any idea what could be wrong, or if it can be fixed?

[FryPpy]

First of all You can try to use "Setup Defaults". To do this go to the BIOS and press F9.
Then you can undo some steps back.
Remove WiFi and test.
Replace SSD with HDD and test.
I don't belive that W8 does such bad things, but i don't use it at all.
May be backup battery (yellow "coin") is dying?