Re: Repairing disks.
Disc fragmentation depends on the age of your computer and the size of your hard drive.
If it is old and has a small, around 10/20/50 Gb hard drive then you will notice it more than if your computer is newer and has a hard drive around 160/200 Gb, I have over 2000 Gb so I will never feel the defragmentation for a long while.
Like Bob says, the defragmentation takes place when you delete/write/download things to your hard drive.
A Hard drive smaller than 100 GB needs to be defragmentated on a regular basis, about a month as your son says.
My computer is now 3 years old and has never been defragmanted but I just did a analysis and it is 1.6% fragmented.
Do a Disk Defragment check ( Start-accessories-system tools- Disk defragmeter) and if it is above 8/10 % on a drive of up to 150 GB then defragment it.
Another way to speed up your computer is to have an external drive(they run slower by the way)and keep your music,photo's etc stored on it so that your computers hard drive will run faster when starting up.
For a back up keep your files photos etc on a memory stick, a 8Gb will store thousands of files Depending on the size of them.