Darren, start by performing the following steps:
-Remove the battery and Power adapter
-Press and hold the power button for 30-45 seconds (with battery and power still removed)
-Insert just the battery and attempt to boot the laptop.
-Insert just the power adapter and attempt to boot the laptop.
If you have more than one memory module, remove one module and try booting with just one module installed.
The other thing I would try is to replace the power cord. Toshiba's are known to blink 5 times with a bad power cord.