The Battery removal for about 10 minutes with the PC powered off, will reset the CMOS Memory (BIOS) back to the default settings.  Reinstall the battery, observing battery polarity before powering back up.   However, you may still have to enter the BIOS (Setup) and reset some items.  e.g. if you do not have a floppy diskette, resetting the BIOS in many models will enable the floppy diskette controller and you will have to disable that and remove it from the boot sequence.  
This Dell Dimension 4600i w Intel Pentium 4 processor 2.66 GHz 512 KB has an issue after I did the clean install of XP Pro with out the drivers DVD normally available but not childproof... My Kid knows everything and found a way into and made changes to the Bios settings, is there some way to restore all the settings back to there default factory settings? Is there a Website to see the settings so I can change them back myself? I have a Dell Inspiron 530 w- Windows 7 sitting and standing by for your help. Will (re)-reinstalling the OS XP Pro restore the settings? The Mouse and Keyboard are not functional at the Welcome splash, yet the keyboard is USB and eventually will work to allow me to tab to login and get me passed the welcome splash and ironically, after it loads, the mouse will next begin to work.  The keyboard does work at start-up, allowing me to open the set-up screen in BIOS. Can this be caused by a incorrect setting in the BIOS?  The nose to the wall child says he changed the settings but cannot remember which ones he changed. (He has been allowed to live another day or two so I might fix this and he is given permission to return to his quarters for sleep) If you ever need to know something ask a young teenager... they know everything... and remember nothing. I Need answers quickly if possible, like A.S.A.P. write me directly, is that allowed? Once I am passed the welcome screen, all seems to be working just fine... Read almost every Q & A page but only find small references to BIOS... I need the equivalent of a MS engineer or better someone who also had this problem, with or without the teenager.  
Updated the Still need help with Dell Dimen. 4600i Bios A07