It is important that the anti-malware products that you use are for on-demand scanning (scanning only when you direct them to do so) and that they don't have any feature activated that performs on-file-access scanning. Otherwise, theoretically even if a virus or malware program is detected, that conflict between programs may cause the virus or malware to NOT be removed. "On-access" or "on-file-access" scanning means that the program that does this scanning operates in the background and scans each file on your computer at the time any other program attempts to use it.
For on-demand scanning of files, I recommend the following free programs:
1. SuperAntiSpyware (FREE EDITION ONLY)
2. Emsisoft Anti-Malware (USE THE FREE PORTION OF THE PROGRAM ONLY). You can download it here. You may have to download and install the "free + full version" (the free plus "pay for" version), but just use (or activate) the free part.
SuperAntiSpyware and Emsisoft Anti-Malware are very valuable for getting rid of malware. Scan your computer with either of these perhaps once per week (alternating which one you use). Emsisoft Anti-Malware appears to be especially good for detection of Trojan malware. You should also very thoroughly scan your computer with it periodically.
DO INSTALL signature updates and free program updates, BUT DO NOT install the "Paid For" or "Trial" or non-free upgrades or updates. (BE CAREFUL IN THE INSTALLATION. THEY MAY MAKE IT CONFUSING ON PURPOSE TO GET YOU TO AT LEAST INSTALL THE TRIAL VERSION, WHICH IS NOT THE NON-FREE VERSION.) If you do, you may be installing an "on-access" or "on-file-access" feature. If you install the non-free upgrades, you may have software conflicts, and in addition to locking up your computer or other problems, you may get virus or malware infection that you otherwise would not.
Whenever you scan your computer with any of these other programs, always scan your computer FIRST with your resident antivirus program. Otherwise, you may experience conflicts, because if a virus is detected and resident antivirus program detects it at the same time, both programs may "fight" over control of the virus (and neither may succeed in its removal), and you may have other computer problems.
A number of "cookies" that are saved to your computer while normally surfing the Internet may be "spyware" or "tracking" cookies. Your resident antivirus program should generally detect especially dangerous spyware, malware, and viruses, but may not detect the Internet "tracking" cookies, that are not so dangerous anyway. (They interfere with privacy, but they don't actually infect your computer.) Firefox (the Internet browser that I recommend) can be setup to delete ALL Internet browser cookies, including all the "spy-ware cookies" or "tracking cookies" when you exit Firefox. Because of this, I personally usually prefer to NOT SCAN with any of the anti-malware scanners (that I have recommended above) while I am surfing the Internet because Firefox will delete all the browser cookies anyway when I exit Firefox. It is the other more malicious spyware and malware that you want to get rid of via the anti-malware scanners.
NOTE: It is best to scan your computer while your computer is idle (while you are not using it) and while the number of processes (outside the anti-malware scanning program) is minimized. This may help in the detection of rootkits, one of the hardest to detect types of malware.
BE SURE TO UPDATE THE MALWARE SIGNATURES BEFORE YOU USE ANY ANTI-MALWARE PROGRAM TO SCAN YOUR COMPUTER.
After scanning your computer very completely with 1) your resident antivirus program and afterward with 2) SuperAntiSpyware, and 3) Emsisoft Anti-Malware, in that order, (with all the updated malware signatures for each), if your computer still does NOT run well, your computer registry may need to be repaired, or there may be other problems. Follow the specific directions listed here.