|Be aware that a factory reset will erase all your persoal files in the process. So if there is anyhthing you wouldn't like to lose, first copy it to external storage; typically dvd, but an external hard drive too if possible. Label and keep the copies safe. Then when the system is working again properly you can copy those files back. Very useful (wise) to regularly copy personal stuff off a computer, so as to have it all safe etc. in event of problems.|
Also check the copies are fully accessible/readable pn at least one other working system, as well as the one that made them - if possible.
This is where to find the manual for your Dell. It will include full details on to most things, factory reset included.
Incidentally, why the need to go for a factory reset? There may be other less drastic options to consider?