What capacitors do I use for an 8 MHz crystal?
Those are 20pF load crystals so you would typically use something like 33pF or 36pF assuming a stray capacitance of a few pF, however Atmel/Microchip does not recommend more than 22pF (or less than 12pF) capacitance so you should choose a crystal with a lower load capacitance (eg. 7pF).
However, with your existing crystal it should start and run okay with 22pF capacitors, but run a bit faster than nominal. If it is not, probably something else is wrong.