How to restore to factory default without operating system disk?

F8 can get an option to boot to safe mode and last known good configuration. If you have a driver problem the last known good configuration is a good option to try. If that does not work then try safe mode. If you can get into safe mode you might have more luck (depending on the root cause of the problem) one can scan for viruses and spyware in safe mode. Sometimes with Vista and Windows 7 you will also see an option that allows you to repair boot up files. That may help as well if one of those files is corrupted. Last ditch chance would be to purchase the restore CD's from the manafacturer. Usually not to expensive. Most places will provide for around $25.00.

It really depends on which brand of computers you are using. For some famous brands, they usually have very good technical supports. You can download the essential files to have your computer rebooted even without the operating system disk. For other cases, like laptop or netbook, the files may also have been pre-loaded on your computer, like my lenovo netbook, I did't even get a disk when I bought it. But the manual instructed me that when there is problem or system failure occur, in which formatting of computer is needed, I can press a F something button before Windows is loaded in order to enter the procedure of rebooting computer. I have tried it once and it is very convenient. The netbook returned to the stage like when I have just bought it. The requires files for rebooting will always be there even when I have formatted the computer (in other words, I can repeat the rebooting procedure whenever it is needed). I think the reason behind is probably because there is no CD-drive pre-installed in the netbook. lol

i don't know much about computers, but this may help. last month we had a lightning strike very close to our home and after that i noticed the mouse on my laptop moved very erratically, the computer was very slow and often just froze. i shut the computer down, booted back up but immediately kept hitting f8 until a screen came up which allowed me to open in safe mode. once there i typed the word restore in the search box and hit enter. that brought me to a screen which (read it carefully)allowed me to start the computer on a previous date. choose a date which you believe is prior to the beginning of your problem. this worked beautifully for me. good luck.