Laptop does not power off after I give shutdown command.

Most of the time this is due to software misbehaving. First update your Dell hardware drivers and BIOS. The driver updates may be difficult if your system will not reboot after installing them - you may need to switch the system off an back on so set restore points during this process. You can get all of the updated drivers from Dell's website for free.

Once your drivers are updated look for updates for your programs. There can be notification area processes (programs by your date/clock like Dropbox, Antivirus, and others) running that are stopping the shutdown. If possible uninstall any applications you are not using using the control panel.

Finally look for viruses and malicious software. You can use multiple tools to make sure nothing is overlooked.

If these options do not work to solve the issue post back and it will be possible to try other steps.