Originally Posted by Dr Goodvibes
I would have placed the battery back in the phone and pressed the power button and see if it booted, or allowed you to get to CWM Recovery with blue light or xRecovery(if installed).
One day, one week. How long does residual power remain in a circuit board to hold the current date/time before resetting?
Maybe buy a cheap BST-41 1500mAh battery for the XPERIA X10 and try that. Could be just a bad battery.
You could check the battery with a multimeter and see if it still has a charge.
My knowledge base stops at this point as I have no experience beyond this.
Update Number 4: Since green Light was always On, I thought what if its in flash mode and much to my surprise, the device is in Flash Mode when I switch it on, how I found out : While flashing via SEUS, I didnt press the back key and the device got connected in flash mode by default, So i narrowed down the problem to something that : My device boots to Flash mode and not as it normally should ? Is it a mother board problem ? Can it be cured ? (god no please not mother board problem) So ? Any thoughts anyone to make it come out f the flash mode. ?