When I try to launch Minecraft, I get an extremely laggy cursor, and a black window where the log in window should be. It's not the "black screen" issue that people talk about, as this is happening before I even log in. I've tried completely removing my .minecraft folder and redownloading the minecraft.exe, but neither of these worked. It's been laggy starting up the launcher on this computer for ages, but it used to work up until recently.
EDIT: My computer is more than adaquate for the game:
Intel Core i5 CPU (second gen I thinK) ATI Mobility Radeon 5650 GPU 6GB dual-channel DDR3 RAM
Only thing that's a bit slow is the HDD, at 5400 RPM.