Excel 2007 : calculate a running total, with a conditional reset?

Hello excel gurus, I need help with a formula: I need to keep an eight day running total. I need to sum the previous eight entries from column A in column B, now here are the conditions - if column A entry =0 then this is a reset and column B =0, if in the last eight entries there is a 0, sum back to 0 in column B.

I'm sure this is simple for you excel gurus, my mind stopped functioning! Thanks in advance.