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#11
There are several factors that affects your shutdown speed in Windows 7. A few I can think right now are:
1. The most common is if you still have a few programs open then it might take some time as the computer automatically shuts the programs down gradually.
2. Secondly if you have a long/custom windows logoff/shutdown sound then the computer wont shut down until it ends.
3. Thirdly some spyware, virus or malware might be running in the background without your knowledge and that might affect shutdown. I advise you to scan your computer once for malware, adware or spyware by using a checker. I have personally used SuperAntiSpyware free edition and it is not bad either.
4. Lastly as you mentioned you are connecting the external hard drive. So, the computer would also check the external drive like any of your other drives and this might also be extending the shutdown time.