gigabyte r9 270x oc not working in x16 slot but in x4 slot

[kamransaeed15]

3 days back i bought gigabyte r9 270x oc and after installing it in my pc it didnt gave any display not even entered in bios so i retry seating it properly but no go both power connectors are properly connected and gpu fans are running but its not giving display i try to change my cable but no go
then i installed it in my another pcie slot that runs on x4 and gpu runs fine without any issue and still working at max performence in this slot
i again tried many times in x16 slot but its not working
ii tried another gpu in my x16 slot and that gpu runs fine but my gpu is not running in x16 slot
i tried every possible thing but no go
plz help me why this is happening as this time my both gpu and mobo are of gigabyte and both are new and they are not working
my pc specs are
core i5 4430
gigabyte b85m d3h
4gb gskill ram 1600 mhz
thermaltake 600 watts psu
gigabyte r9 270x oc 2gb
samsung s20b300 led

[Nelly]

It could well be a faulty PCI-E slot, did you previously use a graphics card in that x16 PCI-E slot, or is it all new?

[V.A.P.P.]

I hope you will find a solution because I have the exact same problem / workaround, different motherboard / videocard but both Gigabyte..

the workaround itself is.. weird.

good luck