Laptop cannot save anything to the hard disk

I own a HP Pavilion laptop with an Intel Core i3 processor, 4GB ram and 500GB hard disk. Recently, after I installed a new copy of Windows 7 Ultimate 64 bit, it does not accept anything to be saved on the drive. I have formatted them but they still won’t work. In fact, sometimes it indicates that a document has been saved on the desktop only for it to disappear when I restart the computer. Your help is appreciated.
