1.) Check the Bios, if the bios sees 250gb, then your good to go to step2.
if not, do like DVR_Expert_Australia said, upgrade the bios, then proceed to step2.
2.) if your HDD is a Maxtor, you will need to go to Maxtor.com and down load the big drive enabler (Very small file). Assuming your Video server is already up and running and has 2 partitions. run the program, tte program will automatically make the correct registry fixes.
3.) reboot your computer once complete running the program.
4.) After windows finish booting up, go to disk management, you will see your remaining space as unallocated. Delete the partition and recreate it with all the remaining space. this entire process should only take you 5 mins and will solve your problem.
below is the direct link to download the big drive enabler and info
http://www.maxtor.com/en/support/downloads/big_drive_enabler.htm