What procedure have you recently used that might create this effect?  For
instance, did you re-install Windows?

The usual reason for this change is that the existing partition has been
removed and then re-created, but it was accidentally created as FAT16
instead of FAT32, and the system has defaulted to the maximum FAT16
partition size of 2Gb.  You can either create an extended partition in the
rest of the drive and then create one or more logical drives to use up the
space (they will become D, E etc) or you can delete everything and start
over, but this time be sure to enable large hard drive support so that
partitions can be created as FAT32.

There are third-party utilities that can change partition size without
disturbing data.
--
Jeff Richards
MS MVP W95/W98