L'Chvod Rabbi Shapiro, Shlita:
1) Are there sins for which Teshuva is not accepted?
2) If so, which ones?
3) If Hashem sends warnings to a person to do Teshuva for a particular sin,
and the person doesn't realize that he's being warned,
and then C"V Hashem sends a physical punishment,
after which the person realizes for which sin he's being punished;
is the person still able to do Teshuva, and would the Teshuva be accepted?