inspiron b130 laptop reset to factory settings

My husbands Dell inspiron b130 has so much wrong with it virus-wise that it would be so much easier to reset the computer back to its factory settings. We have no reset discs of any kind. This had to be done once before a while back and when we contacted Dell they told us how to do it by hitting certain keys on the keyboard. Problem is, we both forgot how. Anyone that can help, it would be much appreciated.