Q I've been using Norton AntiVirus, but after reading last week's review of the free AVG and Avast software, I'm thinking of adding them to Norton for another layer of protection. Should I?

ADon't. Running two anti-virus programs on one computer is one of the surest recipes for disaster in all of Windows computing. At best, each security application will constantly interfere with the other; at worst, the toxic interaction between the two will poison your entire system, and you'll have to reinstall everything from scratch.

That's because anti-virus programs have to do their work among the deepest levels of Windows (that's also why you usually need to replace your anti-virus software if you install a major operating-system upgrade). Having more than one active is like having more than one contractor try to shore up the foundation of a house -- with each contractor working off a different set of plans.

But even if you could run two anti-virus programs at once, why bother? If you have any doubt about the safety of a file you've just downloaded or received, delete it.

Although the risk isn't the same, I also don't recommend running multiple firewall programs on any one PC. They won't add any extra defense against intruding programs, but they'll probably hassle you twice as much when you run legitimate programs.

Doubling up on security software only makes sense with spyware scanners; a second utility may spot a hidden offender that the first missed.

I can't repeat any character when typing without holding down a key for two to three seconds. How do I fix that?

Open the Keyboard control panel and adjust its "repeat delay" setting (in Windows XP, it's under the Control Panel window's "Printers and Other Hardware" category).

-- Rob Pegoraro

Rob Pegoraro attempts to untangle computing conundrums and errant electronics each week. Send questions to The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or rob@twp.com.