Try the sfc /scannow command anyway , and if it askes for the cd , direct it to the C:\windows\i386 folder instead.
And here are a couple of steps to try and run HijackThis. Follow them in order. If one step doesn't work, continue to the next step:
Step # 1
Rename HijackThis.exe to H.exe. Try a scan. If it works, post the log back here. If not, proceed to the next step.
Step # 2
Go to this link and download the 1.98.2 version of HijackThis.exe:
hijackthis1.98.2
Try a scan. If it works, post the log back here. If not, proceed to the next step.
Step # 3
Click here and download Itty Bitty Process Manager (IBProcMan.zip):
ibprocman.
Unzip it to it's own directory and try running it - it will provide a 'taskmanager' like process viewer in which you can stop running processes. Don't stop any yet, just list all that it has so whe can check them and give advice. Post the list back here.