Check in msconfig startup tab, to see if there is a startup item which contains no path to an .exe file.
If the registry Run section contains just the name of an exe file, but by default, Winodws will look for it in the System32 folder. If the entry under the Command column is empty, untick it, click OK, and restart.
Or, if you find under the Command column, an entry with just the name of an .exe file - such as abcde.exe, then go to your system32 folder and check if such a file exists. If the file doesn't exist, untick the box for it in msconfig, OK and restart.
A Creative sound card driver is also known to create this problem. If you think this may be the cause, I'm sure someone can find the fix for you (there's a registry fix on kellyskorner site I think).