Do you like to use your laptop on your bed? Be sure to put a tray, large book, or other hard surface between the laptop and pillows, blankets or sheets. Or, better yet - get a laptop cooler. There are many that double as a laptop desk which is ideal to use while sitting up in bed.
How do I know this? I burned up my own laptop years ago in just this way. Check under the laptop often, whether it's on a hard surface or not. If it's hot, turn it off! Laptops generate a great deal of concentrated heat, which is death to electronics.
If your laptop is running slower and/or giving you strange errors - it may not be a virus or spyware. There may already be heat damage, which, unfortunately, is irreversible.