1. Use Automatic Updates to make sure that security holes are patched to block malicious hackers.
2.Use strong passwords (here) to give your system an added layer of protection.
3.Protect your Wi-Fi wireless internet connection by using MAC filtering (allowing only certain network adapters to see and/or connect to your internet). Also, use the latest form of wireless protection and turn off SSID broadcasting (to give your wireless internet more privacy).
4.Update Your BIOS.
To protect your computer from hackers:
To prevent unauthorized access to your computer, a good antivirus like Avira; which you can get for free (here) and a good firewall is recommended. Windows does come with a good firewall built-in, but a more intense firewall is recommended if you are especially concerned with the security of your computer (a good example of a more intense firewall is Comodo firewall, which you can download for free here). Keeping your computer up to date and installing service packs is also a good safeguard against hackers.
If you suspect that a rogue program is running on your computer and is slowing it down significantly, you can look at all the processes currently running on your computer through the task manager (by pressing ctrl-alt-del) and by pressing on the CPU tab, you can find the process slowing down the computer. From here, you can end the process by right clicking it and to prevent it from starting again, you can find the process on Quick-Start (available here) and uncheck it so that it doesn't start again once you restart the computer.
Restricting the somewhat open access policies that file sharing applications have on your computer can also protect you from hackers as file sharing programs can expose your system to malicious users as soon as you connect to the internet.
However, perhaps the most important way to protect yourself from hackers is to remember to do virus and malware scans on your computer frequently and to delete browsing history to get rid of invasive tracking cookies. Remembering to create strong passwords for your computer is also important for overall computer security as a weak password can be hacked in less time than it takes to type in the password manually!