If you're only getting 35fps on a blank level then that is not normal at all, even my lowest end machine (Q6600, 4gb memory, intel graphics) is getting high 80's on empty levels, my highest end machine (i7, 4gb 960, 16gb memory) gets an fps in the multiple hundreds on an empty level.
What are your specs? \are you trying to run other software at the same time?
i7, NV960 4GB, 16GB memory, 2x 4TB Hybrid.
i5 , AMD 6770 1GB, 8GB memory, 512GB Generic SATAIII + 2TB Seagate Baracuda SATAIII.
i3, Radeon integrated graphics, 4GB memory, 512gB Generic SATAII.
Q6600, Intel integrated graphics, 2GB memory, 180GB Generic SATAII.