One thing to check is that you don't have malware. There is one particular type tgat isn't usually detected buy lives in the temp folder
Goto start, run, and type %temp% hit enter
You will likely see a folder full of random files.
Goto the menu at the top. Goto file and select all.
When all the contents are highlighted hold down shift and delete together.
Answer yes to do you want to permanently delete these items.
Then reboot the pc.
Also if yoyr using Internet Explorer yiu can try going into settings and advanced.
Restore advanced settings.
In Firefox go into the menu and check what add ons are present and plug ins.
A usual suspect is my websearch.
If your using Norton or mcaffe neither are effective.
While norton slows the pc by around half.
I recommend AVG and Malwarebytes anti malware.
The latter will almost certainly uncover any nasties you have lurking.
Beyond that feel free to PM me for further assistance.
IT is my thing so if I can help I will