You don't need a new motherboard because the cards are backwards compatible with PCIE 2 slots.
You're PSU, however, will need to be upgraded.
ok , big thanks , and how do i know if i have the right, 6pin/8pin connections ? i opened my pc case and i saw a bundle of cables,
and i didn't want to unbundle them , but now thaat i know that the cards are compatible with my pc i will look if i got the two 6pins and the 8pin one