I also had this problem - not able to resume after sleep - on my Dell Lattitude E6410 both when running Ubuntu 13.10 and after upgrading to Ubuntu 14.04.
I tried switching graphic driver as suggested by "Lucky" - from the default Xorg NOUVEAU to NVIDIA's latast available driver.
It worked super.
I also had this problem - not able to resume after sleep - on my Dell Lattitude E6410 both when running Ubuntu 13.10 and after upgrading to Ubuntu 14.04.
I tried switching graphic driver as suggested by "Lucky" - from the default Xorg NOUVEAU to NVIDIA's latast available driver.
It worked super.
Regards
Øystein