Toshiba laptop totally dead and won't turn back on...

I've had my Toshiba Satellite Pro R50-B-12V for about 2 years now. About 2 or 3 months ago, whenever I let the laptop go into sleep mode as I've left it for over 10 minutes, it wouldn't start up again. Pressing the power button doesn't work, no fans, no keyboard lights no nothing - all except for the battery light which flashes white. the battery is always charged in these cases, and when I plug in or take out the charging lead it makes no difference to the lights. The only way to solve this issue is to physically take the battery out of my laptop and put it back in and then the laptop will turn on again. this was never a frequent occurrence but now it's doing it every day at least twice a day and once it even turned off and did this as I was using it. No idea what's wrong with it and what I should do. thanks in advance for your help!