PC restarts while playing

AMD stopped driver support for the HD4xxx series, that is why it's complaining about drivers.  The mimimum AMD GPU is listed as an HD5750.  Drivers aside they are pretty close to each other and a fair number of benchmarks actually give the win to the 4870.

The restarting/bluescreens aren't directly related to the game itself.  Could be a lot of things causing it:

Perhaps the PSU doens't have enough juice.  They wear over time and your computer has some age on it.. possible due to capacitor aging.

Perhaps the drivers (the latest 13.9) install is corrupt causing issues.  Uninstalling, Safe Mode, Display Driver Uninstall, restart, reinstall latest.

Perhaps heat related.  Dirt buildup in the the heatsink (GPU or CPU) coupled with thermal paste drying out over time.  I think the white creamique from factory is really only "wet" for a few years then it dries out like a popcorn fart.  Test this by watching heat temps with a program.  If this was the case I'd suspect the fan would be running very loudly.. but perhaps not, default fan control has been something I've complained about for a long time.

Perhaps a RAM module has an error.  MEMTEST86 can test ram.

Perhaps it's an error within windows.  Examining bluescreen logs (bluescreenview is an easy but not to detailed way) might be able to help pinpoint.  SFC /Scannow could help in a situation like this.

Perhaps motherboard is failing (bulging capacitors can be a sign)

If you have any overclocks, definitly default back to stock values.

Try running a demanding benchmark like Heaven or FurMark.  It should stress out your system way harder than PvZ would.  Might help pinpoint whats happening.