Have you considered the possibility that your burner may either be defective
or has a problem with that brand of CD/ DVD? Sometimes a run of blanks is
defective, not all in the box but more than one in sequence.

Can you boot from that thumb drive when it has another operating system on
it? - try Puppy Linux. Have you been able to successfully boot other
computers with those same CD's and flash drive? Some otherwise perfectly
good computers are very intolerant of some media.

How old is the hard drive and is there a functional operating system on it?
Could it have just developed a bad boot sector? Have you run a disk checking
utility?

Just some random thoughts based on my trouble shooting experience. Perhaps
something here might help...