Users have noticed that Windows 7 will delete system restore points after installing applications/drivers and then rebooting.
Slashdot points the way to an annoying bug in Windows 7 that apparently will delete restore points--without prior warning--when the system reboots. The Slashdot post echos what many consumers are reporting on an answers.microsoft.com forum thread found here. Microsoft has addressed the issue with a manual workaround, however there's no official patch, and many users are reporting that the simply fix doesn't work.
In a nutshell, affected users install an application or driver that (seemingly) requires the need to reboot. During the process, the system hangs at the "Starting Windows" screen, and the hard drive remains active. It's believed at this point that the OS is deleting the current system restore points.
"Unfortunately I only found this out when Windows barfed at a USB dongle and I wanted to restore the system to an earlier state," an anonymous writer states. "This is an extraordinarily bad bug, which I suspect most Windows 7 users won't realize is affecting them until it's too late." Many who are complaining about the system restore bug have discovered the issue on clean re-installs of the OS.
One user claims to have fixed the problem using Vssadmin in the command prompt and changing the allocation size on the target hard drive. Microsoft support takes a longer route using a 2-method process, requiring Win7 users to check for the COM+ Event System and to locate DGIVecp.
If you've recently experienced this problem, head to this forum post for both the user and Microsoft fixes.