My guess it that there is just a general (software) problem related to waking up from sleep.
If you want to check this, try going to sleep through the start/shutdown menu or Fn+F1 instead of using the lid switch to confirm you still have the problem to wake up from sleep.
1. I'm not great at fixing software issues, so you may want to ask around more, but if your wake from standby was working recently and you have a Windows System restore point you can use (make sure any important data is backed up first although 'normally' you would only lose any changes made after that restore point date), try setting your system back to this date when things were working.
2. Not sure if you want to disable your lid switch setting so that closing the screen no longer goes into standby mode, but it's possible if you're interested.
3. If you've installed any drivers or software recently, you might try to uninstall them to check/'guess' if they are causing problems to wake from standby.
It's a good idea to stick to the ASUS download site for the approved drivers for your notebook like vga, audio, wireless, etc. if you want to avoid problems.
Don't install any optional updates from Microsoft (no problem to use the critical or important updates for Windws) if they are for your notebook drivers like vga, audio, wireless, etc.
Good luck!
