WAIT! With stand-offs, it is desirable that there be a metal stand-off beneath the mobo at every location that has a mounting hole in the mobo for secure support. But it is IMPORTANT that there should NEVER! be a stand-off under the board where there is NOT a mobo mounting hole! Extra stand-offs in the wrong place can short out a mobo bottom trace to Ground (case). If you look at the mounting holes on the mobo, you'll see small metal "petals" around each one to ensure the screw you turn in there makes contact with the mobo Ground plane. The mobo is supposed to be grounded to the case base plate at each of those mounting holes, and NOWHERE ELSE. Now, this is mainly for grounding out noise stray signals, and actual electrical Ground to the PSU is done mostly by wires in the cables between PSU and mobo, but Ground of the case is also Ground of the PSU.
So, do NOT merely add more stand-offs. You MUST remove any that do NOT match up with a mobo mounting hole, and most often you need to re-locate those to where the mounting holes really are. If you have difficuly removing the existing pre-installed metal Stand-off, try using a small socket from a wrench set, or a nut driver, that has a hexagonal hole of just the right size. This type of wrench gets a much better grip on tight nuts and can give you better leverage than a pair of pliers.