I have read your trouble and as you are telling that you are ineffective to boot from your USB repel. To defeat this trouble just make one bootable disk from your USB repel by copying it in your laptop later on that test to boot from DVD. You can simple boot from DVD. Try this answer I guess it will defeat your trouble and you will not tackle this trouble again. Please let me recognize whether this answer assist you or not? If not then tell me what fault you are tackling.