I encountered this problem yesterday. I found a solution by way of troubleshooting. You will have to get into safe mode with networking and then download the latest wireless card driver.
The main symptom of your Dell computer getting stuck at the welcome screen is due to the fact that there is a compatibility issue with the wireless card driver and Windows Vista Service Pack 2.
Ideally just get into safe mode with networking, get online and go to the Dell.com website. Look for driver updates via support and then find the wireless card driver. It should be updated as of 2008. If there is a newer one, great, otherwise just get the one from 2008.
Install this wireless card driver, restart your computer, you should no longer have any problems where the computer gets stuck on the welcome screen.
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