>>471193depending on how bad the infection is, you may need to backup your data, then either restore to factory settings or reformat. that's a worst case scenario. at least run antivirus scan to check that you're clean
next change your e-mail password.
check your mail settings to check your contact list and whitelist or blacklist haven't been altered
run windows updates and do antivirus scans regularly
keep your browser and plugins up-to-date
use adblocker or aggressive hosts file
and for the love of god, don't go on dodgy sites or run unknown downloads or open unknown e-mail attachments.