I have a Toshiba laptop just over a year old and it did the same thing. I was using it with no problems. Then I turned it off the other day and when I tried to turn it back on the power light came on for about 3-5 seconds then the light went back out.
I jiggled it around a little bit thinking maybe something got lose inside or something and sure enough it rebooted (I don't recommend jiggling it).
When it rebooted it gave a warning about my CMOS battery charge was low so I reset the time and date and saved the changes in CMOS and then rebooted the computer.
Sure enough, IT WOULDN"T BOOT UP AGAIN!! I was upset because I'm a very seasoned computer specialist, this is what I do for a living. And I couldn't figure out what the heck was going on.
So I went to the Toshiba site and of course my pc was two months out of the 1 year warranty (figures). So I went about checking to see if I could download the manual for the pc.
Normally the manual is a simple download or online PDF file but not here! It asks you for your model, serial number and then it checks that your out of warranty. Then it allows you to try to download and install the manual, asking again for a model or serial number.
I went through this stupid download, install and tried to run the dang thing to get the manual only to be notified that the program couldn't find the serial number! Something like invalid serial number entered.
I realize I'm a little off track here on this one but the dang manual was not accessible after three attempts of installing, uninstalling the stupid program with out any success. The website was very helpful when it came to estimating the amount of money they would charge me just to look at the thing (around $130) and on up from there. NO THANKS!!
So I decided it was time to break the case open and see what I could find. To make a long story short I pretty much tore the whole thing apart and examined every cable, component and part of the laptop that I could with out actually removing the motherboard itself.
Couldn't see anything really wrong like broken components, motherboard cracks and or lose ribbons, cables, and it didn't appear that there were any burned components either.
So I tried booting it again while it was open and I noticed that even the fan wasn't turning. I had a power light, had it plugged in but same thing not even POST or CMOS was being read.
So to conclude: I noticed a spot where the normal CMOS battery would be located but never could find the actual battery. I have seen them located underneath the motherboard on other occasions, and couldn't refer to the user or system guide (thanks for nothing Toshiba), so I finally went ahead and disconnected every ribbon, cable, and component inside the computer.
Still couldn't find anything visibly wrong anywhere on the system and so I went ahead and reinstalled the motherboard, reconnected every ribbon/cable and component inside the computer and told myself that I finally met my match and was then beginning to consider what parts I could salvage from this darn computer.
So I buttoned everything back up and for the hell of it gave it one more reluctant try to power the darn thing up and wouldn't you know it, IT BOOTED UP!!!!
So there you have it. I never could find the CMOS battery, but for some reason taking everything apart and reinstalling everything back together solved the problem!!!
So if you feel confident enough to disassemble every part of your Toshiba laptop (not a lot of people are mind you) without a manual or assistance of any kind from the manufacturer then have at it. What's the worst that could happen, it doesn't boot up so its useless to you as is so give it a shot and good luck.!!! Worked for me better than any of the other "expert" solutions offered everywhere else.