There are two possibilities...maybe three
1. There is nothing on the usb stick. ****
2. You are not booting from that usb stick. This needs to be specific
How to Enable USB Boot Option on Dell Inspiron N5010 1.Restart the computer and press f2 while starting up. This enters the setup program. 2.Select the Boot tab and change to Legacy Boot, Secure Boot Off. After restarting, this shows the boot sequence and the order can be changed using +/- keys. 3.I then change the boot order to. CD/DVD. USB drive. Hard drive. To specify the boot sequence: /Start the computer and press ESC, F1, F2, F8 or F10 during the initial startup screen. ... /Choose to enter BIOS setup. ... Use the arrow keys to select the BOOT tab. ... /To give a CD or DVD drive boot sequence priority over the hard drive, move it to the first position in the list.
This from :
3.If anyone here has a Dell (@wizardfromoz
may be of help, here)......they will surely know the procedure