"Invalid BOOT diskette"....error...Dell rig

Ok..so it's not exactly a hot rod here.
Im putting a little rig together for my mom using my older Dell Dimension Lr 500mhz. ( Hey it was free what can I say)
I re-installed WinXP Pro. So far so good.
Computer boots way too slow for fresh install I thought..takes 2-3 min.
Then at times during boot up....and past bios screen....I'll get the message: " invalid boot diskette"....insert disk into A:\.......When I ctrl/alt/del.....it will reboot fine to WinXP.
Boot order is: HD/Floppy/CDrom
512mb PC133
I ran a scan check on the HD...and it checked out.

What can this be?

I would check and redo all your HDD and Floppy cables, if that does nothing try it without you FDD installed and see what happens.

Also might wanna hit it with a fdisk /mbr.

Could be a controller problem as well. Sometimes the drive is recognized by the bios other times it isnt. Try setting it to manual rather than auto. Like Semyaza said check the connections as well and any jumpers and cables.

hit f2 (i think it is) and get into the BIOS. The just load up the default settings and that should fix it. I had this exact problem today on a machine and it took me FOREVER to figure it out lol. Live and learn.

FYI, BIOS is usually Del (Delete) but it'll say "Press x to enter setup".

Do you have a floppy in the drive?