Since this computer is now 9 years old, expect the worst. Make sure you have all of your 'can't afford to lose' files backed up onto something other than this hard disk, preferably CD, or any external hard drive or memory stick. If the hard drive fails and you have not done so, you may lose everything you have collected and stored over the years.

That done, tell us whether you have a firewall installed, and if so, which one. Is the firewall turned on?

Also, tell us if you have been using any Registry Cleaners, or Optimizer type programs. We often see damage to the registry after using such programs.

Next, open the System Configuration Editor (MSCONFIG). To do that, goto Start > Run, type in msconfig and click OK. In the new window, goto the Startup tab. Look down the list and de-select any entries that you don't need. We can't help there because we can't see your list, but all you need are any Microsoft entries, the firewall and the anti-virus. Anything that looks suspicious, use Google to check the entry.

Next, update both AVG and Malwarebytes' Anti-malware, then reboot the computer into it's Safe Mode and run those two scanners one after the other in safe mode. How to enter Safe Mode? Restart the computer, and just before Windows begins to load start tapping the F8 key lightly once a second. A list of Safe Mode options should appear with Safe Mode at the top. Press Enter on the keyboard to load Windows in this mode. Many viruses and malware cannot start in safe mode and so cannot hide themselves, and this is a good way for thorough scanning.

Assuming that comes up clean, reboot normally and then run the system's "Disk Cleanup" utility, (Start > All Programs > Accessories > System Tools > Disk Cleanup). Note that when it opens there may be a short delay whilst it checks for compressed files. After that, delete all temporary files and temporary internet files.

Next step, Check Disk and Disk Defragmenter. These are both long running utilities. I mean, they will both take a long time to complete.

ChkDsk - Open My Computer and right click the C Drive, then select Properties. Open the Tools tab and click the Check Now button. The system 'should' tell you that error checking cannot be done now whilst programs are running, and offer you the option to check at the next restart. Select that, then restart the computer. The ChkDsk should run and check the whole of the hard disk. This will take some time. Do not interrupt the process.

Defragmenter - When ChkDsk has completed and assuming it either has found no errors, or found errors and fixed them, run the Disk Defragmenter. Before you do that, turn off any screen saver and disable other running programs like the anti-virus scanner. Do not run any programs. Then return to that Tools tab and click the "Defragment Now" button. Again, this will take a long time.

Do not use IE, and I would suggest you do not use Chrome. Instead, download and install Firefox, and then install the following Firefox add-ons, NoScript, WOT, (Web of Trust), and AdBlockPlus. All of these will help Firefox identify suspicious web sites and web components that may affect your system.

See if any/all of that improves performance. But beware, if the system is about to fail or the hard drive is on it's way out, you need a plan to recover, either by reinstalling the operating system on this drive, or getting a new drive to do that.