Q I switched my Dell PC from Windows Vista to Windows XP in order to go from a dial-up Internet connection to a faster broadband connection from AT&T. Now I want to go back to dial-up access to save money, but I can't make XP work with the modem. I keep getting a "692" hardware error message and no modem dial tone. What can I do to make the modem work? Or, if I removed Windows XP, would Vista come back so I could easily use dial-up?

ED MEYER, KEY BISCAYNE, FLA.

A The error code 692 just means your modem isn't working. It worked with Vista because you had a Vista-compatible software driver pre-installed on your PC.

To make the modem work with XP, you need to download XP-compatible driver software. (You can get someone to download it, then transfer it to your PC with a portable flash drive.) Ask Dell to tell you the modem's manufacturer and model number so you can find the right website, then search for an XP driver for that modem.

Uninstalling Windows XP won't bring Vista back; you'd have to reinstall it with the Vista disk. But back up your data first, because it will be deleted.

Q When I try to change my PC settings back to the way they were on Aug. 9 using Windows System Restore, I get a failure message. Why did it fail?

DEAN REINKE, MINNEAPOLIS

A One of several reasons.

Is System Restore turned on? (To find out, and turn it on if necessary, go to Start, Control Panel, System and System Protection.)

If it's on, your ability to roll your PC back to an earlier time will be limited to the dates on which "restore points" were created. Windows generates restore points at regular intervals, or whenever you install new software.

But restore points are saved for only 90 days, and Windows may delete some restore points sooner if it needs the disk space or for some other reasons. For details, go to support.microsoft.com/kb/301224.

Q I use a Wi-Fi wireless router at home, and it has a built-in firewall. Will that protect my PC, or should it also have a firewall?

RON LASSOW, BLAINE

A Safe computing requires that every computer have its own firewall. Find the free ZoneAlarm firewall at tinyurl.com/5vtzry.

Note: Several readers reported trouble with the "tinyurl" substitutes I use for long Web addresses. Remember, you can't type them into Google or any other search engine; instead, type them into the Web browser's address window.

E-mail tech questions to steve.j.alexander@ gmail.com, or write to Tech Q&A, 425 Portland Av., Minneapolis, MN 55488-0002. Include name, city and phone number.