Depends what tools you have at your disposal.
If you are getting blue screen its most likely going to be one of the following -
1.Faulty RAM - I had a computer last week that was BSOD and turned out to be RAM.
2.Hard drive - bad sectors for example can cause BSOD.
3.Software fault - a virus, or some corruption somewhere.
4.Motherboard fault.
5.Over heating - if its over heating then probably it will probably occur only after its been on for a little while, then once it happened once will keep happening.
If the laptop is staying up for at least some length of time, then download and run this tool -
https://www.passmark.com/products/bit.htm
Run just the RAM test first of all, and it should give you errors if there is a fault with the RAM, or it may crash whilst running in which case its also likely the RAM.
If you have a spare hard drive then you can put it in the laptop, and load windows on to it (easy way to test without having to back up your data first). If it fails then you know its RAM or motherboard. If it installs fine you know that the problem was either with your original hard drive or your software.
Basically its a case of troubleshooting each possible cause.
