Please help,

I connected my computer to the Net and soon after noticed that an icon called "download software" was appearing on my desktop. I followed the path and discovered a 'MSA64CHK.dll' file in system32. I deleted this file as it is related to adware etc... The icon is no longer present, but an error pops up just before my desktop loads up saying that it cannot find the "MSA64CHK.dll" file, thats because it has been deleted.

What to try???