I had a very similiar problem when i bought a mircophone for Strat. battles and i needed days to find a solution. I am not sure if I am helping you, but thats how i get my mic. working.
I use a Lenovo PC which comes with an "onboard soundchip". That soundchip needs a special driver from Lenovo for working probably , but when I installed Win. 7 on my computer, a Windows sound driver was installed over the Lenovo driver without my knowledge. That results in a similar output signal you have. So i replaced the the Windows sound driver with the newest Lenovo sound driver and suddenly my mic. was workable.
So if you use an "onboard soundchip", maybe it helps to visit your computers (or motherboard) manufactor homepage and look for the newest sound driver.
