Q: The hard drive on my Windows 7 PC is inexplicably using more storage space than before, even though I haven't added any new programs. The hard drive is storing one to two gigabytes of additional data every week. What's causing this?

Clarke Cordes, Lakeland, Fla.

A: There are several reasons your PC might be storing more data, some of them serious. First, the worst-case scenarios:

Your PC could have acquired malicious software that is using up disk space. Run the free Malwarebytes security program (see tinyurl.com/n7q3t28), and make sure that your PC has current antivirus software.

Your hard drive could be failing. A disk drive error can cause some storage areas on the disk to be ­corrupted. The PC automatically avoids the corrupted areas and stores data elsewhere, causing more disk space to be used. You can find out if this is the problem by running the Windows Disk Check program. Open Windows Explorer and right-click on the C drive. From the menu, choose "Properties," then click the "Tools" tab. Click "Check now," then choose "Automatically fix file system errors." (Attempting to fix corrupted areas of the disk is a separate action that takes much longer to run.) When prompted, click "Schedule disk check" and restart the PC. For details, see tinyurl.com/qyxwf2x.

There are other potential causes that are easy to fix:

Your disk could be storing unnecessary files, such as Web pages that were kept by a browser. Run the free CCleaner program (see tinyurl.com/djpqzx) to eliminate unneeded files.

Your Windows System Restore feature may be keeping too much old data. System Restore lets you return your PC's settings to an earlier date within the last three months (called a "restore point") so you can reverse undesirable software changes. But you can remove some older restore points to save disk space. Open CCleaner, click "Tools," then "System restore."

Your disk drive might need to be defragmented to store data more efficiently. As your disk fills up, the PC splits files into fragments that are scattered around the disk in available storage spots. Defragmenting consolidates files at one disk location and unused storage space at another, which makes it easier for the PC to store large chunks of data. Go to "Start," type "disk defragmenter" in the search box, and click on the resulting icon. In the program, choose "Analyze disk," and, if necessary, "Defragment disk."

Q: I do a backup of my PC's C drive to an external hard drive. If my C drive crashes, can I copy both programs and data from the external drive to a new C drive?

Jerome Sturgeleski, Minneapolis

A: No, you can only back up data files to an external hard drive. To prevent people from making multiple copies of copyrighted software, PC programs can only be installed from an authorized source, such as a software disk or an Internet download.

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