What is the operating system and service pack level; e.g. Windows XP Home Edition Service Pack 2 (SP2)?
What is the make and model number of the computer, if brand name; e.g. Dell, HP, Gateway? If not brand name computer, what is the make and model number of the motherboard?
After you reformatted the hard drive, what did you use to re-install the operating system? Did you reload from the vendor provided Recovery Partition or Recovery CD? Or did you reload from a "retail" or OEM Windows Installation CD?