The Program is Located by opening the start menu then clicking Accessories> System Tools> System Restore is on this Menu
All you do is select:
Restore my computer to an earlier time then the " Next>" button
and a calendar will be shown .The Highlighted dates are the Restore points
The Window alongside tells you what major changes have been made and "Software distribution" service is perhaps a none indexed Item/s Which the Computer makes for any update
If you wish to adjust the Size /date range then on the Left hand frame of the Systen Restore window
You'll find the settings link which open up a window with a slide bar I cannot tell you what to set this at (depends on your Hard-drive size
Personal Preference)
Reading from the Top There is a Tick box to disable System Restore
You Want it enabled... Untick this
Now the Slide bar this is simpler than it looks to set up
The Maximum you are allowed is 12% of the Hard-drive capacity However you may have to keep peeking at the SYS Restore calendar to see how far Back that will take you
I have a 160GB drive and My setting is 3% which is about 2 Months Restore Points
Top tip Start at 6% and give yourself 1 to 2 months "space" as your Target
Click the Apply then the OK buttons to Save the setting
And setting the Bar at 0% is pointless
Have a really Big Disk drive then The slider must be set as low as possible @ 1% Going to have Several Months restore points due the Programs Design

and of course Pulling the Bar to Maximum is going to save places for "several years"!
This is from the Windows Help to System Restore.The
highlighted 2nd section has info about where to look for clues on the Calendar

The
Red Highlight is what I think has Happened to you
quote:
To access the System Restore Wizard, click Start, point to All Programs, point to Accessories, point to System Tools, and then click System Restore.
Antivirus utilities can affect whether your system can be restored to a previous point. If a restore point contains an infected file because the utility is not set to clean the file within the restore point, or if an infected file has been removed from a restore point by an antivirus utility because it could not be cleaned, System Restore will not recover the computer to this partial or infected state. If System Restore could not restore your computer to a previous state, and you suspect that one or more restore points contain infected files or have had infected files removed by the antivirus utility, you can remove all restore points from the System Restore archive by turning off System Restore and then turning it back on.