Here is a list of free resources to use to fix and maintain your computer or anyone elses for that matter. All of these are 100% free to download and use.

Free Anti-Virus Software

Never install more than one anti-virus on your computer as they will conflict and they wont work properly

Anti-Virus is a must have software on any PC running windows. Anti-Virus software protects you against the threat of viruses infecting your computer. Once a virus has infected your computer then it can replicate itself to other computers, steal your personal information, hold your system to ransom and and make your system not work properly. . There are many good free anti-virus solutions some of them are:

Avast
Avast has a free version of there anti-virus with one feature that is very good called boot time scan, as the name says this runs a scan at boot time before starting windows. Avast does use a fair bit of system resources though so I wouldn’t recommend this for old or slow computers.

Microsoft Security Essentials/Windows Defender
This is built into windows 8 (Windows 7 you need to download and install it) and is very good for older slow machines as this software has a low overhead and doesn’t need to much power to run. Very simple program and because its made by Microsoft it updates through windows update so no extra update tools required.

AVG
A quite popular anti-virus, has a free version. Over the years it has become quite heavy with lots of options and I wouldn’t recommend this for a old or slow computer.

Free Malware Removal Tools

Malwarebytes
Malwarebytes free version is a malware scanning tool that scans for many different sorts of threats and then lets you choose which ones you want to remove, this is a personal favorite of mine as it picks up most threats and will remove them.

Combofix
Combofix is a free tool that automatically fixes lots of malware and virus related issues. Make sure to follow the link above to download the software. There are some sites that claim to offer Combofix, but really give you a piece of malware instead.

The initial screen you see when you run Combofix looks a bit suspicious because it tells you to power off your security software, but it is legitimate. Although I have not had problems with it, there is a chance that Combofix will crash your computer so always back up your data first.

TDSS Killer
This is a rootkit scanner that scans for TDSS rootkits. It is really quick to scan and I reccomend using this during any virus removal.

Free PC Maintenance Tools

CCleaner
CCleaner is a utility that cleans out your temporary files. These files can build up on your hard drive and cause your system to slow down over time. This utility also has a registry scanner that finds old registry keys and can delete them for you. It asks you to back up your registry before deleting any keys, always do this just in case it causes problems then you can restore the registry. (I have never had to restore the registry after using this tool but its always better to be on the safe side.

Revo-Uninstaller
Revo as the name suggests is an uninstall program. This envokes the built in uninstaller and then scans for any left over files folder and registry keys that the built in uninstaller has missed. You will be surprised how much some programs do leave behind.

Defragler
It is a good idea to defragment your hard drive every now and then. Defraggler is a free tool that easily and quickly defragments your hard drives. It is hands down much better to use then the defragmenting tool built into Windows and shows you how much is left and gives you more incite then the Windows one.

Free Operating Systems

Ubuntu
Ubuntu is a version of Linux that is quite user friendly and a good version of Linux to learn on as there is a ton of support for Ubuntu on the net with all of the information on forums it is more than likely someone has had whatever problem you have before and people on their forums are always willing to help a beginner. Don’t download the server version either as this has no graphical interface and you will just have a command line.

XUbuntu
XUbuntu is a version of Ubuntu that is designed to run with less memory so it is good for laptops and old computers that have trouble running normal Ubuntu or windows

Here is also a list of password recovery/bypass tools.