Wojtek,
What version of BIOS are you using?
If interrupts are not disabled, you should still be getting the Timer interrupt. The default is Hwi14. Can you make sure that the Timer interrupt is still being generated! Otherwise your TSK_sleep would never wake up.
Are you able to use ROV to view the state of the system? Make sure you HWI and TSK stacks do no overflow. After that it would be checking the KNL mask and readyQs to make sure they are not out of sync.
Judah