Tell us the Dell model number, and age.
You may have a failed hard drive, or other problems.
You might want to see if it will boot to <SAFE MODE> which you access by pressing the <F8> key repeatedly once per second soon after you press the <ON> button.
If it starts to boot, give it plenty of time to finish creating those low resoultion screens.
If it boots to SAFE MODE, then you have a start on fixing it, and you can get back to us.