another plus 1 for Adblock Plus and Quick Java if you use Firefox, you say you have win 8.1 so you must have IE 11 and IE has never been very competent at blocking popups in any version.
before you go chasing ghosts make sure your Java is up to date the latest version is 7 Update 45
Verify your version
get the latest free version of CCleaner. version 4.09.4471 is up now but that might change by the time you read this. install it, you can check/uncheck items you want to keep or delete, click Run cleaner.
if you must use IE then go into Internet Options click on the Privacy tab then look for Pop-up Blocker click Settings under Blocking level: select from the drop down box High: Block all pop-ups
if after all that you still get inundated you probably have some malware installed or are you just surfing really dodgy warez/porn sites... lol
run an online antivirus scanner, make sure you disable your resident scanner
ESET Online Virus Scanner is probably the best one out there now Bitdefender screwed-up theirs
there are other things I could tell you to try but I need to know what browser you are using and the sites in question.