edit: You should check the BIOS to see if it lists your hard drive, and if it does, attempt to reinstall windows or attach the drive to another computer and try to get your data off of it.
Typically, there is a removable panel on the bottom of the laptop (4 or 5 screws holding it in place) for the hard drive, and the drive pulls out pretty easily by pulling it way from the connector, then up out of the laptop.
You can replace it with any new 2.5" SATA hard drive (get the size you want). SATA 2 or 3 are both ok to use, and will run the same speed. Getting a 7200RPM drive can make the laptop a little zippier (assuming you didn't have a 7200RPM before).
If you don't need much storage space, an SSD hard drive will make the computer MUCH faster; a 128GB drive will cost about 100$ give or take a bit, and they go up in price from there.
If you want any advice on what hard drive or SSD to buy, just post back.