I am glad to know the computer is again booting to Windows.
Internet connection could be slow because of Virus, Spyware or Malware in your computer. Please ensure your computer has good anti-virus software and anti-spyware program such as Malware Bytes or SuperAntiSpyware.
Another recommended fix for the problem is to update the drivers for the network adapters (both Ethernet and wireless). Safe Mode uses Fail-safe drivers that are guaranteed to work properly.
Try the above mentioned two fixes and do reply with results.
To know more about Dell's products, services and drivers & downloads, please go to http://dell.to/YBlak6
Thanks & Regards