IF a Blue Screen of Death (BSOD) happens once, then you reboot and keep working and not see it again. Just shrug it off.
If you get a repeated BSOD, then look at the 0x0...... error code. Lookup the error code on google as this can help with troubleshooting.
Any new applications/services installed?
Have you run a full malware/virus sweep on your system?
Have you Run a memtest?
If you suspect memory, try removing half of the mem and running to see if BSOD appears. Now try to the other half. this is a method to ID flakey chips, but a Memtest is better.
Just after your bios has completed and before windows begins to load you need to press F8. This will bring up a menu. At the beginning of the menu is the option "safe mode". Select safe mode and see if the computer will boot.
If it still wont boot the your problem is more likely to be hardware related.
If it does boot fine then your problem is more likely to be software related.