To repair all Windows system files, at an elevated command prompt, put in sfc /scannow
That's probably not the only issue however, the infection may have cleared out the registry entries that load the services. If System Restore isn't available, you may be stuck doing a re-install (the other option is a repair install but those are usually messy enough afterwards to warrant a re-install).
I wish there were a true repair install for Windows that did not involve re-setting many of the connections that programs have made in the registry.
EDIT: If you know exactly which services are missing, you can copy the registry entries from another Windows install if it's the same version (I mean Vista or 7 or XP, the variations between each of those (Vista and 7 Basic/HomePremium/Ultimate/etc and to a lesser extent, XP Home/Pro) usually don't matter.