For the diskette drive 0 seek failure, does the computer skip past this error without difficulty ? If it does, then you may ignore it. It is caused probably by your replacing the battery having reset the BIOS which is thinking now it should find a floppy disk to boot from. If you haven't a floppy disk, or have floppy disk drive you will get this message. I do, but I ignore it. When you power up, you could try entering the BIOS setup, by pressing for example, the esc, F1, F2 or F8 keys - for your model I don't know which, you may find out from the internet, your manuals, or the Dell website/help or support - repetitively before the computer starts,
( from Dell support - "You can enter the system BIOS or Setup on a Dell PC by pressing F2
at the Dell loading screen").and somewhere the BIOS setup there should be the boot order change this to CD first (no CD inserted unless it is bootable), then USB if available (no media USB inserted, some USB devices are ok), the HDD. You should not set HDD first because this will give you big problems if it goes wrong and you need to boot from somewhere else. Put floppy disk after HDD and the message will disappear.
I don't know about the password issue. I suggest you contact Dell support on this topic.
You may find the following links helpful
and have a good look through this page
and the associated links. In subsequent efforts try joining the Dell Users group (or what ever it's called, probably accessible from the link above and asking there, it might be a common issue that many have experienced and there are well known solutions to)
Sorry not to have been able to answer your questions directly, and to have pointed you in the direction of lots of reading, but I hope the links prove to be quickly useful