Tried Guide but nothing will run

Pretty sure my son downloaded somehow(within the last 24 hrs)...anyway started having problems with searches being redirected (firefox) and then noticed my avast antivirus was off...tried restarting it, received error tried repairing, then uninstalling still won't start...tried Spybot and it won't load, again uninstalled reinstall same thing happens...start searching the net and come across the malware guide...followed it (including ccleaner before starting the windows xp cleaning procedure)

downloaded all programs as instructed

installed SuperAntispyware, updated and scanned...after scan there was 1 infection in files (something about Trojan/GenA) it quarantined and removed it and asked me to reboot so I did...went to start it again to get a log and a box came up saying "Windows cannot access the specified device, path, or file. You may not have permission to access the item." Tried the Alternate start and nothing happens (get the hourglass for a second then it disappears, not in task manager processes)

installed Malbytes (renamed downloaded file too)...started quick scan and then it disappeared (also from task manager processes)...tried running it again and got the "Windows cannot access..." like with Superantispyware

started Combofix...I got a loading type thing(rectangle filling up with Combofix written above it) it just about finishes filling up and then disappears, waited 10 minutes, checked task manager/processes it's not there...try starting it again and it tells me the install failed and to reboot and try again...tried again and it disappeared again

installed RootRepeal...started scanning files (noticed it said 2 things hooked) and then it too disappeared on me...tried restarting it and got "Windows cannot access..."with it too

MGTools started and then it too disappeared on me

also noticed in task manager processes grep.cfxxe running now

Any help would be appreciated thanks and hope I gave the right information