Have you perhaps changed any hardware recently (new memory?), or perhaps installed some new software.
It can also mean the PC is too hot. If it happens just after boot up them maybe one of your fans is not working, or maybe the fans or heat sinks are clogged up with dust.
It sort of depends on you ....
there are a couple of things you could try ... but if you aren't "into" PCs it could be a bit frustrating.
(sorry if this sounds patronising ... it's not meant to - but if you not used to this sort of thing it can be hard work
normally a BSOD at startup is due to either ... bad drivers or bad hardware (the chaps will be wondering what else it could be;-)
so the first step is to startup in safe mode ...
(which can be difficult to get the timing right)
startup your machine .... and then start pressing the f8 key (dab dab dab not preSSSSSSSSSSSSSSSSS)
if you get it right you'll see a black screen witha menu giving a few options ... go for safe mode.