Do you have a Windows 7 or 10 installation disk available?
If you don't have a Windows installation Disk you can download and create a bootable Windows 10 DVD or USB from:
https://www.microsoft.com/en-gb/software-download/windows10
Then, try booting from the Installation disk and select the 'Repair your Computer' to access the Recovery / Advanced Options tool menu and select 'Command Prompt' option.
In the command prompt window run the DiskPart program and enter the following commands:
- Enter "List Disk"
- From the list of disks displayed note the 'Disk' number numeric
- Enter "Select Disk number" where number is the numeric you noted previously e.g. "Select Disk 0"
- Enter "Clean"
- Enter "Create Volume simple" (if this throws an error message, ignore it)
- Enter "Create Partition" and follow the instructions to set the partition size to maximum
- Enter "List Disk" to show the disk size, hopefully 250GB !
If the problem persists, another option is to consider updating your PC BIOS to the latest version by visiting your PC manufacturers support web page as suggested via OCZ support faq:-
http://ocz.com/consumer/ssd-guide/ssd-faqs