A complete tutorial can be found here: http://www.digitalcitizen.life/my-pc-has-nasty-virus-now-what-how-do-i-remove-it

1. Priority 1: Data backup
Priority 2: Disinfection
Priority 3: Recovery
Priority 4: Prevent further damage
My PC has a virus.
Start disinfection:
Cleanup
worked?
1.1. Backup your
data
Stop
No
2.1. Create
antivirus recovery
drive
2.2. Boot infected
PC from the
recovery drive
2.3. Clean the PC
using the recovery
drive
Yes
Entered Safe
Mode?
3.3. Reinstall
Windows
3.6 Recover your
data (if backup
available)
3.7 Reinstall apps
3.4 Install a good
antivirus
3.5. Scan your PC
1.2. Create a Live
Disc
1.3. Boot Live Disc
1.4. Backup your
data
No
3.1 Boot into
Windows
4.1 Scan with
another antivirus
for a second
opinion
3.2. Verify your
data & apps
4.2. Change your
passwords
Yes
No