You may not have unmounted the drive properly the last time you used it. The file system may be corrupt.
You can run "sudo /sbin/fsck.vfat /dev/sda1" on it (assuming it is assigned the same device).
Or if the filesystem is OK and you can mount it graphically, do so. Then either enter "mount" by itself, or examine the contents of /etc/mtab. Both will list how it is mounted and the options used.
You didn't post what the mount command was that you tried. You may not have had the mountpoint created or didn't include the filesystem or device or options.
I would recommend connecting the drive, and (if it is assigned to /dev/sda1 again) entering: udevinfo -q env -n /dev/sda1
This will give you information about the UUID of the filesystem and the filesystem label if it has on. Use one of them instead of the device name for removable drives.
Here is an example using a pendrive:
Oct 14 19:41:02 hpamd64 hald: mounted /dev/sdc1 on behalf of uid 1000
From mount output:
/dev/sdc1 on /media/disk type vfat (rw,nosuid,nodev,noatime,flush,uid=1000,utf8,shortname=lower)
udevinfo -q env -n /dev/sdc1
The filesystem doesn't have a label, so I could either label it or use the unique filesytem id (UUID) in /etc/fstab
I'll just make one up here, taking the easy way by copying the same options that the auto mount system used:
UUID=3B69-1AFD /media/pendrive vfat rw,noauto,user,nosuid,nodev,noatime,flush,uid=1000,utf8,shortname=lower 0 0
You could use your username instead of your UID in the uid= option. You can also finetune the permissions with the fmask and dmask options. See the "mount" man page for details. The /media/pendrive would have to be created. Note the "user" option. This would allow me to mount it without having to use sudo. If this drive is normally connected, you could even add a "mount /media/pendrive" to your .profile or .bash_profile files so that it is mounted when you login.