Double click Spyware Doctor's icon from the desktop, press and hold CTRL+Shift+Esc -> go to Processes TAB, can you see swdoctor.exe in the list?
Make sure you do not have other internet security softwares blocking Spyware Doctor's .exe files. If they did block Spyware Doctor's process, please allow the file: swdoctor.exe and update.exe into the whitelist / ignore list.
Finally try to download the latest build of Spyware Doctor installation file from
www.pctools.com and then reinstall using this installation file.
cheers,
riFFz