Start with the basics for laptops.
Windows power plan set to "Performance".
All power savings features turned off.
Battery needs to be plugged in.
Are you on the correct drivers for you laptop? Laptop graphics update...How to
Have you followed the steps listed here? How to Configure Laptop Switchable Graphics
If you have done all of this and are still having the same problems, I suggest you contact Dell for assistance. As there seems to be a much greater problem with the system.