Is it the same memory (same specifications)? Mix/matching memory specifications doesn't always work well.
Did you verify the memory is compatible with the motherboard?https://support.gateway.com/s/PC/R/1014670R/1014670Rsp3.shtml
The machine will support up to 8gb of ram as per these specs.
As mentioned the RAM may not be compatible with either your board or your old RAM.
For a start take out the old RAM and stick in only one stick of new RAM in the slot the old RAM was in.
If you can boot ok then try adding the other new stick in the same channel. If this is ok then your board can use this Ram. But is likley unable to use the two kinds together.
Next try a single stick of of new and a single stick of old RAM and a single stick of new RAM in separate channels.
If it doesn't work swap the channels and try again.
If it still doesn't work then I'm afraid you can't use the new RAM with the old RAM.
If it does work try adding one stick stick at a time of remaining RAM.
If you can get to 3 sticks but not 4 then it may be a power issue.
I borrowed 4gb of ram (U-MAX 2x2) and i put it in my pc and it recognize it as only 1Gb. i tried both slots and it still said 1Gb each. Thts weird.