I have been struck down with it three times in the past, twice warranting a reformatting of the hard drive (before I found this forum).
After you get infected, DO NOT reboot! I suspect PS Guard replicates itself in this process. Run Ad-Ware and other anti-spyware programs to get rid of it as much as possible. Then manually look through your directory for any folders with "PSGuard" in its title and delete. Also run CCleaner to clear as much crap as possible.
What is left of PS Guard should be in your Registry. You got 2 methods to approach this:
(1) Use Windows' System Restore to reset the system to a point in the past when you had no PS Guard infection, OR
(2) Import a backed up Registry file to clean up the Registry.
If you don't have a valid restore point or a backed up Registry file, apologies. Back to the experts in this forum.
I have used (1) myself and managed to get rid of PS Guard. So it is tried and true. Good luck!