500 GB Samsung hard disk suddenly stop working. Please help me.

If it won't work, recovery software won't work either. The only way to get data off it when it stops working is to send it to a data recovery service which is very expensive.

That's why you should copy all your important data to at least one additional hard drive or to optical discs when the drive is healthy and working, because all hard drives fail sooner or later.

There are options to try to access a failed hard drive. If it didn't give any warning like noise or initial trouble, there's a reasonable chance it may still be accessile to recover your data. When they initially fail, disabling the S.M.A.R.T. BIOS setting may allow it to boot... If that doesn't help, other options are to try to access it from a new installation or another computer as the Slave drive if IDE or second drive is SATA or even from a USB enclosure. If none of the suggestions work (may be recognized but no data may show on it), try running CHKDSK on before attempting again.

Sometimes the S.M.A.R.T. BIOS setting on some motherboards is so strict it can prevent a perfectly good Hard Drive with a temporary issue from booting. As an example; I have an old 120GB IDE Western Digital HD that my newer system didn't recognize till I disabled the S.M.A.R.T BIOS setting, I now have it running on an older computer and I occasionally check it with the application Hard Disk Sentry and it reads it as in perfect condition... so go figure what the BIOS programmers had in mind(?) but more importantly imagine how many users lost their recoverable data because they quickly gave up.