CD/DVD won't read (by 2 users)

I have a dual boot 2000/XP system. This issue only occurs on XP and only recently without any changes to BIOS or XP system config.

1. I have CD and DVD master E:\ slave F:\ drives. If I boot with E:\ loaded, E:\ can read/write. If I then load F:\, it cannot detect a disc in the bay. If I open then close E:\, it still reads the disc in the bay. If I removed the disc, close E:\ then open and reload the disc, it no longer reads the disc. Still nothing on F:\

2. If I boot with E:\ empty and F:\ loaded the situation is reversed from number 1, above, i.e., F:\ is readable initially and E:\ is not. After opening and closing F:\ bay, it is no longer readable.

3. If I boot with both E:\ and F:\ empty, neither is readable.

4. If I do a hard boot with both E:\ and F:\ loaded, both are initially readable. Open and close F:\ an it become unreadable.

I have a custom machine: XP SP3; 2.4 gig Athlon 64; 1.1 gig RAM; both ROMs are TDK; the master/slave HDs are on the primary, the master/slave ROMs are on the secondary IDE.

It may be unrelated but I have also noticed lately the my modem (ZOOM V92) tends to freeze if I connect after I've been using other hardware devices like the ROM or scanner.

I am wondering if the BIOS IRQ assignments are all of a sudden not to XP's liking??

Any thoughts would be appreciated.

Thanks, Monk