Hmm, it doesn't sound right. As a test, I've just switched my N810 off then plugged it into the charger. Without pressing the power button, plugging in the charger causes a white background with a large word NOKIA on it to appear, then after a few seconds that disappears and the screen is mostly black except a charging symbol in the middle. I don't see the flashing white you're seeing.

I only got my (brand new) N810 a couple of days ago, and I saw the same thing when I plugged it into the mains for the first time, so I don't think what you're seeing is normal for a brand new unit, even if the battery is fully discharged.

If you know anyone else with an N810, or any other device which uses the BP-4L battery, you could try their battery just in case your one is dodgy and isn't able to be charged, otherwise I think you may need to get a replacement/refund for the N810.