Please try this: turn off your computer. Then turn it on, and right after the black screen with white text or the computer company logo disappears, press & release key F8 repeatedly until a menu appears, then you select Safe Mode with Networking (note: if there is no menu, then try the same steps again, but this time, press key F8 a bit earlier). Then login and click Start->all programs->accessories->system tools->system restore and restore the computer to any date before this issue has occurred. (Whether system restore works or not, please continue the next step below.)
Next, please go to Safe Mode with Networking again, then click below and click on Download Latest Version, to download and install the Malwarebytes Anti-malware software. Then scan your computer: http://www.filehippo.com/download_malwarebytes_anti_malware/
(don't buy anything; just use its free feature.)
If needed, please click Start, then click on Run only if available, then type msconfig and press Enter. Then click on the Startup tab and uncheck all the boxes, except your antivirus/security program. Then click OK, and restart the computer and check.
Please let me know if there is still any issue later. Thank you.