XPS 400, keyboard misstrikes ONLY while on-line, help!

my keyboard misstrikes (certain keys do not respond, not always the same keys) ONLY when I am on-line.  it performs perfectly while in WORD or whatever.  I have a wireless keyboard and mouse but I also tried a "wired" keyboard with a USB wire and the exact same result.  I received a whole new set (keyboard, mouse, etc) from DELL and it did not help.  also, I reinstalled the relevant drivers, to no avail.  I've deleted recent software that may have messed things up, no help.  I have run virus, spamware, firewall, etc, continuously since I bought my machine in 4-06.  I "think" it is some kind of "setting" problem.  I've tried the "Internet option" tab while on-line and it does not seem to be it.  please, HELP, someone, it is driving my wife crazy (she's taking an on-line class and has to look at the keyboard to type).  thxs.