Don Homan's hard drive crashed the day after his laptop's warranty expired. What should he do?
Besides curse the fates and the laptop manufacturer?
If you don't have an up-to-date backup, your first priority will be getting your data back. Depending on how you use your PC, that could include business documents, photos, music, email, and so on. Several companies specialize in recovering data from broken drives. I hesitate to recommend one because I've never needed one myself and there's no practical way to test them. But I can say that Ontrack and DriveSavers have long and mostly positive reputations. Recovery could cost you thousands of dollars, but that's the price of not backing up.
If you decide to get into the backup habit, see What's the Best Way to Backup What I Need to Backup?
So, on to replacing the drive, itself:
Assuming it's a standard laptop SATA drive, physically replacing it should be easy. I can't give you exact directions because they vary from one company and model to another, but replacing a laptop hard drive is usually pretty simple. Check the model's documentation or the manufacturer's web site.
Restoring Windows is another problem. Every Windows computer comes with some sort of recovery tool for restoring the operating system. Unfortunately, most of them these days come in the form of a special partition on hard drive. If you didn't get a recovery disc (and possibly even if you did), the recovery tool is gone with the drive.
If that's the situation, call the vendor and see what they have to offer. Best case scenario: They'll sell you a recovery DVD for $10 or $20. Worst case: They'll insist that you return the laptop, so they can install a new, reimaged hard drive at a considerably higher price.
As a future precaution, I suggest you create an image backup of the hard drive, which you can use to restore the operating system without depending on the manufacturer's recovery tool. See More on Image Backups for details.