Normally, if my work is for someone else, which is always pro bono, if the standard tools of the trade doesn't fix things, if recovery disk set hasn't been created, I'll make these. And will collect an inventory of all installed software with Belarc Advisor. plus make sure that the latest drivers are already on hand.
Then will copy anything that person wants over to a Flash drive, where during the next step, these will be scanned with a few tools to ensure they're clean. Sometimes it's so bad that I'll advise to nuke it all. So once the recovery disk set has been created, I'm off to the races with a re-install. If this were my computer & knew what was going on, I'd use the inbuilt Recovery partition, as I re-install every year to 18 months as a form of cleanup (it shows too, with a nice speed increase & more responsive). Better than the unsafe Registry cleaners by far, some of which may leave all unbootable. However, it's always possible that the Recovery partition can get infected.
After install, I update what drivers can be done before updating, then off to that, after this is complete, with the few reboots in between, I'll finish installing any drivers, check Device Manager to ensure all devices has drivers. Then will remove any junk software installed on the computer. And will then defrag, run a combo AV+AM scan with the Emsisoft Emergency Kit (same engine as Emsisoft Anti Malware, a dual purpose AV+AM scan), and perform 1st backup (this one, I always keep & advise everyone to, it provides a clean install at anytime). Once that's done, will run Extended Disk Cleanup & reboot, install all (or most) software that was installed prior, defrag & backup again.
I'll then install any subscription based security software (if present), if not, will install Avast Free Antivirus normally, and Malwarebytes Anti Malware (free version) & call the owner to pickup.
Note that while this is considered a shotgun approach, there's no doubt that the OS is clean when it leaves my place, before it leaves, will also let it sit and run a Custom scan with MBAM, all options selected, as well as a boot time scan with Avast (an exclusive feature of that brand). During the boot time scan, it searches places it can't while Windows is running. Much like some paid defrag software, the boot time defrag ensures the page & system files are defragged. BTW, that's what I defrag with, and download & install a Perfect Disk Trial on their computer. While this may seem time consuming, it's really not. By the time I've spent over 12 hours running various tests & am still infected, I can have most of the way freshly installed the OS clean.
Plus if I needed to post in the "Am I Infected" section, that's 3-5 days gone. And as posted above, the speed and response improvements are worth the efforts.
And if the infection is severe (normally or often the case), I tell others as I practice myself. In such a case, that computer is no longer trustworthy & no way would I even check my email on it, let alone make a transaction (well, really it's been almost 3 years since I have made a transaction on a Windows OS). Linux MInt has been my "go to" OS for over 5 years.
Note that since most of my work is pro-bono, there's no $100-$200 shop charge involved, yet I'm often rewarded with many things, such as fresh veggies in the season, a 3 year old monitor or possibly notebook when a new one is purchased, and other items. So it pays to give.
Plus I enjoy helping others, regardless of whether the folks can give back in return or not, it doesn't matter to me. The ones who gives to me in return for repairs are those whom are too tight to pay for the services. There are others I assist, in particularly seniors/disabled, who cannot afford to pay, nor give anything, and I expect nothing. I do spend a little more time with these folks on education in smart computing practices, and you know what. Seldom does these call on me again. They're more likely to listen, have good attitudes & I'm happy to assist these because of it. Oftentimes their infection came at the hands of a relative or friend, not what they done.
In this case, I create an account with limited rights, this helps greatly with infections, and the visitation of unauthorized sites. 18 years old & below Web restrictions covers a lot of ground.
In fact, I have a reinstall of Windows 7 to do Sunday for a senior.