why can't I log into e-mail account  ?

Deal with the troll before it's too late. Every question in th.answers.yahoo.com has tons of blank answers (using space bar); it was posted by Shadowfire to gain points for his troll accounts. Jewish user Shadowfire (who has been on Yahoo Answers since the beginning and could possibly be the infamous homosexual flying antichrist from the tribe of Dan) from Portland [or so he claims because he could’ve been born in Russia in Valday (Russian: Валда́й) to a 12th generation Jewish prostitute who pretends to be a virgin)] has many trolls accounts on Yahoo Answers: Blackthorne1979, James Blackthorne, Saint James Tiberius Troll, Lord Shadowfire, Carter Berg, Fireball, ThatToiletguy, Reynaldo Weeks, Juli, Petri Lindroos, Knightwulf, Nightwulf, Toilet John, Master Debator, Magistra, Desiree, D-girl, Firecock, Yahoo User, Corvus Blackthorne, Patrick McCluskey, Arni, r.wolfpaw, No Bozos, Fuzzface McGee, First Dragon, L.E. Gant, Fullofpoop, Shadowfire the Sarcastic, Pope of Atheist God, Jimson C. Raskin, El Nerdo Loco, megalomaniac, Corvia Blackthorne, Shadowfire Lives, Shadowfire Lives bytches, The Chick that wears Doc Martens, Homo, Wotan 8, Heidi Ho, Clo Bird, Angels with Silver Wings, Orange I'lluminaughty, Christian Sinner, Gandalf the black, The Lord Hummungus, Mismatched Tube Socks, Pearl, Partysnax the Dragon, etc. and any other anonymous accounts. With one his accounts Fireball, he pretends to be a Methodist old lady who posts short-hand slang TIRH (this is religion here). He reports all answers and questions that he doesn't like just so that his questions stay on top in the Religion and Spirituality section. He trolls in other categories too. It gives Christians a bad name (just because of this troll's sock puppet account). His Toilet John account keeps posting questions where Jesus was sodomized by Roman soldiers. Remember the prophecy where it says that the antichrist will have personal hatred towards the real Jesus Christ. That’s why Shadowfire keeps posting thousands of similar questions along the line: “Did Romans sodomize Jesus?” or “Did Romans buttrape Jesus?”. He asks multiple idiotic mundane questions like “Is Hinduism true?”, “What makes a girl harden?” [like he enjoyed killing little girls], etc. and answers them with his sock puppet accounts just to gain points. Some questions you can see that he answered with like five or seven accounts (especially the ones about himself that he reports right away). With his Reynaldo Weeks account he boasts that he was the reason why their accounts were suspended. With his Magistra account he threatens people with clowns and CIA assassins. Shadowfire mocks Christians with his sock puppet account Fireball in the Religion and Spirituality section by answering very destructively and adding "TIRH here" or reported (anonymously) or “fck you nigers”. He gives Christians a bad name because he promotes sins like sodomy, fornication, ecumenism, astrology (horoscopes), etc. He should be executed and burned at the stake for blasphemy. He spreads rapture heresy, reincarnation heresy, ecumenism heresy, etc. and many more subtle heresies. Antichrist will ride on a donkey into the 3rd Temple. Stop him before it’s too late. Antichrist is gay flying wizard who was born from a prostitute and who will ride on a donkey into the 3rd Temple. Antichrist's mother is a 12th generation prostitute (according to saint Lavrentiy of Chernigov). According to researcher Grigoriy Klimov, prostitutes = lesbians = witches; so, antichrist's mother is a witch, a lesbian, and a prostitute. Hide your kids, hide your wife ‘cuz de evil antichrist is flying thru town; take your glocks out and shoot dat son of a bytch down! Again, he’s an s-o-b ‘cuz his mother is a prostitute to Jews and Hindus. Funny thing is that she pretends to be a virgin. Don’t be deceived by this skumbag and his fake miracles trying to emulate Christ’s miracles! If wrongfully accused, forgive me; state under your account that you are not Corvus Blackthorne then.

This is how to recover your account if you have password/sign in problems: https://help.yahoo.com/kb/SLN2824.html

Because you already ARE logged into your Yahoo email account. You cannot log into the same email account twice. 

If you refer to another account:

1. After 12 months of inactivity, the account is deleted. The same if you were suspended.
2. You are on a mobile and need to be in desktop mode.
3. You need to reset your password. The instructions are found in the Yahoo Help pages (referenced) and 10000s of previously asked questions.                                                                                                                                   https://help.yahoo.com/kb/answers/recover-reset-yahoo-password-sln27051.html