I'm running an ATI 5770, an Athlon II 2.8Ghz quad core CPU, and 4GB of RAM.
Up until about 2 months ago, everything I played ran fine - specifically, League of Legends and Starcraft II. (NOT demanding games in the least, and other things like BFBC:2 ran great as well)
At some point (not sure when or what I would have changed to caused this) I started getting slowdown - sporadic in LoL, constant down to 40 in crowded settings in SC2. Since then, I've taken all the steps normally associated with this sort of thing; nothing helped so I wiped the HD and re-installed Windows (Win 7) I'm on the latest service pack with all updates, have the latest GPU drivers, and furthermore just pressure-cleaned the case with an air compressor. I've been monitoring heat and my system stays at a constant ~24-27 while my CPU goes up to ~45 if I'm trying to push it.
In any case, none of this has helped with my fps issues. What other steps can I take? I'm really hoping it's not a hardware issue.