I'm having exactly the same (or at least almost the same) issue.
I have x220 with 4Gb RAM in two slots, WiFi+WiMAX, Camera, Bluetooth, IPS screen and Win 7 Home Premium SP1.
Fingerprint, Express card and WWAN are not installed.
I have all the latest software installed.
The problem is:
Some times notebook doesn't want to wake up from a sleep state. If I open the lid (if it is closed) or press Fn button (if lid is open) notebook tries to wake up - it blink ones with CAPs lock, light WiFi LED. The power button continues it;s slow flashing. There is no HDD activity, but I hear fan noise. Screen remains black.
NB remains in this state while there is an energy in a battery, after that it start beeping (help!help! I'm out of energy

), but it still not responsive to any mouse-button movements. I have to power down the system, of course on a next boot windows complains that is was not powered down properly.
Same thing also happens (not always) if a timer wakes NB from sleep to put it into hibernate.
I'm not able to identify the roots of such behavior - It may hang both after pressing Fn+F4, or after closing the lid or after timer, i.e. any "go to sleep" actions may cause problems at resume. I failed to create a scenario which guarantee problems during resume, the behavioral is unpredictable. I can have one failure just 10 minutes after reboot and not to have them after 20 sleep-wake cycles in 2 hours.
Windows logs show no errors. I tried different power schemes, tried enable/disable "hybrid sleep", tried different USB and PCI power management parameters, still no luck.
Any advise?