Can't boot after running CCleaner

Did you allow CCleaner to back up before hand?

When you clean your registry it would have asked you if you wanted to back up first.

Yes Ccleaner does have that prompt unless the user turns the prompt off.
Default is the warning/requests in on/activated.

Enable the hidden Administrator account from a Win 7 install DVD (WinRE)

See here: User Account Password - Change from WinRE

See if you can boot to Safe Mode (press F8 at boot) and login as Administrator.

If yes, open Windows Explorer and navigate to your normal login accounts My Documents folder and find the backup, it will be called something like cc_20140816_231827.reg, which is

cc_yyyymmdd_hhmmss.reg

Right click on it and select Merge to add the entries back into the registry.

Reboot and if that was the cause of the problem all should be well.

You can try this then:

Boot the install DVD and take the Repair path to get to a Command Prompt then do the following:

cd c:\windows\system32\config
ren system system.sav
copy regback\system system

This puts the last backedup copy of system in place of the current, messed up, system.

Exit and reboot, see if that allows you to login. If yes, try a System Restore now, even though it did not work before it may work.

Note that C: may not be the right drive letter for your boot drive. It's often different when you boot via DVD or flash drive. To find it, enter bcdedit from the Command Prompt. Output will be something like this (what mine looks like)

Code:

>bcdedit

Windows Boot Manager
--------------------
identifier              {bootmgr}
device                  partition=\Device\HarddiskVolume3
path                    \EFI\Microsoft\Boot\bootmgfw.efi
description             Windows Boot Manager
locale                  en-US
inherit                 {globalsettings}
integrityservices       Enable
default                 {current}
resumeobject            {6a5e5b97-6999-11e3-be70-40f02f1a4b14}
displayorder            {current}
toolsdisplayorder       {memdiag}
timeout                 0

Windows Boot Loader
-------------------
identifier              {current}
device                  partition=C:
path                    \WINDOWS\system32\winload.efi
description             Windows 8.1
locale                  en-US
inherit                 {bootloadersettings}
recoverysequence        {6a5e5b99-6999-11e3-be70-40f02f1a4b14}
integrityservices       Enable
recoveryenabled         Yes
isolatedcontext         Yes
allowedinmemorysettings 0x15000075
osdevice                partition=C:
systemroot              \WINDOWS
resumeobject            {6a5e5b97-6999-11e3-be70-40f02f1a4b14}
nx                      OptIn
numproc                 8
bootmenupolicy          Legacy
usefirmwarepcisettings  No

The default entry under Windows Boot Manager points to the default boot partition {current}.
Find identifier {current} under Windows Boot Loader, the device entry there points to the drive letter you need to use, partition=C: in my case.

If this doesn't help, just del system and ren system.sav system to get back to where you are now.