Observe if your normal internal browsing is getting slower or not. Check out for any unwanted toolbars that may be installed without your permission. These toolbars display annoying advertisements and make internet surfing a lot slower.
Go to Settings in your browser, and click on toolbars to identify all toolbars installed on your computer. One of the indicators of spyware presence on the system are the windows that pop up randomly when browsing the Internet. Some other symptoms are the flickering of your screen, applications are taking ages to load, and some random changes to your browser and desktop settings.
Download and install a malware search tool on your computer. You may either install the Microsoft Malicious software scanner or get your hands on a third party application for scanning your computer. It will scan the whole computer and display all detected spywares. However, it will not remove the spywares itself, you may either have to manually remove them or install an Antivirus for that purpose.
There are many spyware prevention programs that stop them from causing any effects to your computer. The complete solution for all PC problems, though, is an Antivirus suite. Purchase a paid subscription of any antivirus program, and keep its virus definitions updated at all times.