Dim 2400, with XP 2, one gig memmory and TWO Seagate hard disk of 250 ea.

A few days ago I noticed the second HD storage was no longer on My Computer list. On System Info the disk is gone a so is the letter asigned to it. The other two drives got their letters moved up also. Going to device manager and disk manager it show right and says it is on line, active and healty.Also on system info it shows on Disks but not on Drives. What can I do?ALSO right clicking on the disk bring a menu without the "change letter"option.

PLRASE, PLEASE, somebody help me.