Random Sleep Mode/Shut Off?

[Nrein]

I've been having this issue since yesterday, though it initially went away after awhile yesterday, only to come back to haunt me today.

For technical know-how, here's a quick sum up of what my Laptop is;
Toshiba Qosmio X775
Core i5 Processor
Nvidia GTX 560m GPU
6 GB RAM
640 GB HDD
Owned for less than a year.

When I would turn on my laptop, it kept randomly turning off. This could be anywhere from five seconds after turning it on (how it was when I first tried) to minutes. Longest I think was 15? Anywho, by instinct I figured it was either a virus, overheating, or some sort of hardware issue. I did a scan, nothing. I checked my laptop for burn smells/burn spots, nothing. I ran different diagnostics, nothing. Up until I did a hard drive check, where I found there to be numurous errors. After having my program fix them, it seemed like the issue had stopped.

But now today, it's doing the same thing again. But this time, instead of just going straight off, for quite a few times it's been going into sleep mode. And that's how the laptop has apparently been trying to shut off, by going into sleep first, but then it seems like it's just forced straight to power down. I've since then been monitoring how hot my laptop has been getting, but I've been barely reaching anything near a high temp. AND I doubt it could be overheating, because it's been shutting down/sleeping while doing simple tasks, like Firefox, or just sitting here. But I managed to play graphic-intensive games for hours with no issue at all. I also ran another hard drive test, but found no errors at all this time.

I'd really rather not have to send my laptop in to Toshiba, because I can neither A.) Back up my hard drive here just in case they replace it, and B.) Don't even think I still have the warranty. And yes, I've tried googling for this issue, but I've found results that are either unrelated, or aren't for this specific brand of Toshiba Laptop. (Found similar issues on older ones, but neither this model or newer ones.)

[WingedZephyr]

Are you sure your laptop battery isn't dying? Sometimes laptop batteries can lose their ability to hold a charge; I've had that issue with mine. The laptop would probably work fine as long as it's plugged in if that's the case though.

[Nrein]

Yeah, I know that batteries tend to do that, but I've already checked. I've tried it with just the battery on, plugged in with the battery, and not with any battery at all.

I also have a handy-dandy battery checker, so I would know if that was an issue.

To sort of update, the issue didn't persist as long today as it did yesterday, but it was a bit more intense. It seems to only happen around the time I initially turn on the laptop, but after awhile it goes away. Tomorrow I'll probably do a RAM check, see how bad the cache could be clogged from all the sleep/hibernation I've done since I've owned it.