Perhaps the most significant turning point in Queen Victoria's life was the death of Prince Albert in December 1861. His death sent Victoria into a deep depression, and she stayed in seclusion for many years, rarely appearing in public. She mourned him by wearing black for the remaining forty years of her life.

Albert's death came suddenly. In November 1861, he contracted typhoid fever. He lay sick in bed for several weeks, finally succumbing to the disease on December 14. He was only forty-two years old. Victoria was devastated. She wrote to her daughter Victoria shortly afterwards: "How I, who leant on him for all and everything—without whom I did nothing, moved not a finger, arranged not a print or photograph, didn't put on a gown or bonnet if he didn't approve it shall go on, to live, to move, to help myself in difficult moments?"

The Queen turned mourning into the chief concern of her existence the next several years. The Prince's rooms in their residences were maintained exactly as he had them when he was alive. Her servants were instructed to bring hot water into his dressing room every day as they had formerly done for his morning shave. She had statues made of him, displayed mementos of his around the royal palaces, and she spent most of her time secluded in Windsor Castle or in Balmoral up in Scotland, where she had formerly spent so many happy times with her husband.

After the first year, her mourning came to be viewed by many in Britain as obsessive, and public unease arose about the Queen's state of mind and the state of the monarchy generally. This unease was aggravated by Victoria's refusal to appear in public except on the rarest occasions. She made her first public appearance only on October 13, 1863, and then only to unveil a statue of Albert at Aberdeen, Scotland. She appeared publicly in London on June 21, 1864, riding out through the streets in an open carriage. She did not personally appear to open Parliament until the 1866 session, and then only reluctantly.

Source: http://www.sparknotes.com/biography/victoria/section5.rhtml