I'm using Avast at the moment, and got a BSOD. Then I ran Avast but it didn't find anything viruses. What could cause a blue screen? Everything is working as usual... after restarting it and I didn't lose any data.
Anything under the sun can cause a BSOD. I could sit here all day listing possible reasons for a BSOD but it won't matter.
If you just get the one BSOD then it's probably just a error with windows itself or a momentary and single error with the computer.
If you get multiple BSODs at regular intervals then you may need to start looking at problems. Often it can be solved with a physical cleaning of the computer (dust and other dirt can accumulate and block airflow causing overheating), or a windows reinstall (particularly on old installations, not turning off your computer properly can also lead to early OS "death").
Other times you're not so lucky and need to go through and test system components such as the CPU, RAM, GPU ect.
But there's no need to worry about any of that if it's just a once off.
As long as you need mostly office and web browsing, and gaming isn't that important to you, Linux is the best! Open Office for linux - it can open/save .doc files though.