rahmu wroteThe usb drive is bootable, I tried it on other computers and it worked... anyway thanks for your concern, I'll see how I can fix this.
Try hitting esc once your PC boots so that you get a menu that shows from which medium you would like to boot your PC, the flash drive option should be included,other options that are included are the CD Drive and hard disk actually that worked for me when i had the same problem as you. Furthermore, some older PCs may not support booting from USB actually i have another fairly older PC that is not able to do that... Anyways, good luck and i hope it works :):)