With the restore CD that came with your laptop. If you no longer have it (or never did) you can get it from Asus support. In some cases you can even download it as an iso and burn it to a CD if you have acces to a 2nd computer. That way you're not waiting on Asus and the mail. If you're in the US: http://www.service.asus.com/ If you're someplace else: http://www.asus.com
On those old Dell laptops you can "reset" them by unplugging it, removing the battery, then the RAM, replace the RAM then the battery. This can clear all kinds of minor glitches. However, if the problem is of a more serious nature then you may have to contemplate cutting your losses and getting a new laptop as this one is worth less than it would cost to have it repaired professionally. I wouldn't work on this laptop if one of my customers brought it to me other than checking for simple way to fix it. I'd encourage them to let me salvage date off of the hard drive in order to move it to a new laptop. Good luck.