Instead of replying, addison60334 accidentally reported this thread. I'm posting his intended reply here:
My problem is solved. I eventually wiped my precious programs from the HDD and it suddenly started to behave normally again. I assume that one or more of the programs was corrupt and preventing the browser menu from appearing.
The problem, mentioned by many people, about the liteon rejecting blank DVDs also gave me trouble, but after using 8X or 4X discs instead of the more usual 16X, this problem is cured.
Thanks to Mr. Belvedere for his comment.