Is it under warranty still?
How old is it? What brand ?
maybe it is just a lemon?

Is it too late to ask for a replacement?

We had bought an HP/compaq laptop last fall but within 18 days it was doing some odd stuff- restarting itself for no reason, blue screening etc.

The in store return policy was 15 days, but I asked about leniency on the date as it was only a few days after.
the manager on duty was willing to work with me plus there was a $125 rebate involved for buying the laptop- I didn't want to lose that - it was part of the reason I bought it.

anyway they did an exchange for me and since the $125 was over they did it as a gift card to me, so I didn't lose that.

PS - the second laptop has been working great.