Until recently my laptop took at most around 5 seconds to go to sleep when the lid is closed. This was the case for several months. Recently however, my laptop takes around 2 minutes (maybe more) to go to sleep whenever the lid is closed, or when the sleep command is issued. When the sleep command is issued, the screen fades to black, and the computer becomes unusable until it goes to sleep. This happens most of the time now, but sometimes it takes 5 seconds as it used to, if I'm lucky.
This issue has suddenly started happening, and wasn't a gradual thing, so I think there's a specific thing that's causing this issue, and not just a result of slow "computer rot" or whatever.
This is pretty unacceptable to me because I would want to make sure it's sleeping before I stick it in the bag or whatever, and it also seems like a waste of time. The problem is I'm not sure when exactly this started happening, so I can't tell if it's caused by an update, or by a USB device I plugged in, or whatever.
Waking up from sleep is as fast as it was before, taking at most 2 seconds. So no issue there.
Are there any ways to identify the cause on why it is taking too long? It seems to me that Windows is waiting for a driver, service, program, or device to respond before going to sleep, so I'd like to find out what that is exactly.
If it matters, I'm running Windows 8.1 64-bit on a Sony Vaio Pro 11.