DOS box with c:\winnt\system32 appears

You'll need to check your registry for an invalid entry. See here for full details:

http://tinyurl.com/2n7j

Maybe this is a login script if you are connected to a network.
Check C:\winnt\system32\repl\import\scripts\*.*

This absolutely sounds like a login script. However you probably won't find the script at the location Florinel suggests. If you are connected to a network then the login script will most likely be on the server at %systemroot%\system32\repl\import\scripts, or at %systemroot%\system32\repl\export\scripts. The easiest way to find the script, if you have the proper permissions, is to open Network Neighborhood, open the server, and then open the NETLOGON folder. The NETLOGON folder is the share name for the scripts folder mentioned above.

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