I have the owner bring in the USB stick and DVD media to test boot in other PCs. Too often it's just a bum DVD or USB stick. We remake it for them and send them on their way. The next problem is usually pilot error. That is, the owner didn't set the BIOS to boot from those devices.
I own a Dell Inspiron n5110 2011 manufactured (Core i5, 8GB) laptop. When I plugin USB stick it shows in read-only state in last few weeks. When I tried to boot from Windows DVD/USB (to reinstall windows) it doesn't booting up from the DVD or USB. Other than this laptop is functioning normally even though it is little older.
Does anyone know the reason for this or a way to fix this?

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