This just happened to me, after a bad odin back-to-stock trying to fix some problems the phone just turn off, no screen, no leds. The phone is dead, canīt access to download mode either. I change the usb cable but didn't show any sign of life. After about 30 min of giving up, I tried pressing the Turn On/Off + 1 buttons, trying to access Download mode several time just hoping it magically works, and suddenly there it is, Download mode. After that, phone is working.
Not sure is this would help, but it least I tell me experience. Good Luck.