Strange behavior - related???

[photographer]

In the past two days my Mac is exhibiting strange symptoms - first Mac Mail kept losing the password to retrieve mail from the ISP server and I had to keep inputting it manually. Today I was burning DVD's of photographs. After the burn I tried checking the disks but the machine rejects them ( 3 separate tries on different disks.) The DVD's load perfectly on my G4 iBook and the burns are good. I tried some disks ( both CD's and DVD's) of older burns and they load fine in the desktop.
I'm not only confused but worried that something major might be happening - any suggestions?
Thanks,
jay