Malware Mess - need help devising removal strategy

I need some strategic help, please. My daughter's Dell Studio 1747 (Windows 7 64 bit) had a cracked LCD screen which I replaced. I backed up her machine to her older sister's 2 TB external hard drive before the repair. After I replaced the screen I did some maintenance on the laptop and found a lot of malware, including a number of versions of Trojan Alureon. I've followed the advice on this website and am now down to 4 "partially removed" Trojans according to Microsoft Scanner. In addition to that problem, the Dell Pre Boot System Assessment indicated a 2000-0142 error in Hard Drive 0, which I believe means the laptop hard drive is unreliable. The laptop is still under warranty so I can have Dell deal with the hard drive issue, but I'm trying to save the data on the laptop and get the known malware off of older sister's external hard drive.

So to recap I have a laptop with 4 partially removed Trojan Alureons and a dodgy hard drive, and a 2 TB external hard drive with a back up of my younger daughter's badly infected laptop, and a back up of my older daughter's laptop.

A few questions:
How do I disinfect the external hard drive? Do I have to delete all the data or just the files from the infected laptop?
Is the laptop with the partially removed Trojan Aleurons safe & secure, or do I have to completely remove all traces of them? And if so, how? (I've run Malwarebytes, TDSS, Rogue Killer, Hitman Pro, MG Tools and Microsoft Scanner).

Thank you.

And yes, my younger daughter is in BIG TROUBLE for not surfing safely!

 

Hi Tim:

I've been able to clear the viruses/malware, and then ran Dell diagnostics - the computer needs a new hard drive and Dell will replace.

I have a simpler question for you now - I did scan the external hard drive and it appears to be free of malware. However, what's the best way to be sure? I don't need any of the files that are on it so I can reformat or do whatever it takes to make sure it's 100% clean.

Thank you so much for your help.

 

Thank you. And thanks for all the info on this site - you're providing a great public service. Much appreciated.