Interestingly, it looks like the L45-S7423 is not on the list of laptops supported by Toshiba for upgrade to Windows 8. However, before upgrading to Windows 8, I ran the stand-alone Windows 8 compatibility checker from Microsoft and it found no issues with the laptop.
Be careful because Microsoft's compatibility checker may not identify all the problematic hardware.
So, I will have to investigate if this laptop will run Windows 7. If not, I guess I am stuck with a dead end Windows XP operating system or will have to move to a Linux variant.
It seems the issue is more related to the driver update from Microsoft site. I recommend performing System Restore first. Then, you may prevent installing the hardware driver updates from Microsoft right now.
Its better to buy the laptops which are fully compatible for Windows 8.1 upgrade with signed drivers. Few laptops can be found here for 300$ and 500$.