I had this issue on an old laptop once, and I somehow managed to get past it by unplugging and replugging the hard drive, but it only worked once. This may work, otherwise you could try a recovery tool (I Forgot My Password, etc). Otherwise, you can try professional data recovery, but if you don’t need the data, then you can replace the hardrive or format it. Windows formatting:
[quote|format=featured]Open ***Disk Management*** (type diskmgmt.msc in the Run dialog).[/quote]
Right-click the drive and select "Format."
Follow the prompts to reformat the drive
If you need the data, it will be hard if not impossible to get past the password. You may be able to plug it into a different device, which may prompt the hard drive encryption to bypass the password using the previously cached information.