It impacted different sectors at different times. Most real estate developers in California agree that it began in 2005, and most software engineers in Silicon Valley say that it began when the dot com boom went bust during the late 1990's, which was later compounded by the World Trade Center attack in September 2001. It was further compounded by the Iraq war, the Afghan civil war, Hurricane Katrina in 2005, and by adjustable-rate mortgages because they ballooned. Finance professionals who work in the inter-bank credit/lending business say that it started in 2007. In 2008 The National Bureau of Economic Research said that it began in December 2007.
The Great Recession actually started during the 1980's, which I'll explain in a moment. The dot com and real estate booms during the mid to late 1990's were a flash in the pan. 1991 was a very bad year. Silicon Valley grew during that period but the rest of the Bay Area suffered. The East Bay was in financial crisis. Contra Costa County was in such grave condition during the early 1990's that the residents had to commute to other counties. They worked in San Francisco, Alameda County and Santa Clara County. At that time the president was George Herbert Walker Bush, but the Great Recession started even before he entered office in 1989.
During former President Ronald Reagan's tenure, the nominal national debt rose from $900 billion to $2.8 trillion, largely due to the Cold War between the U.S. and the Soviet Union (the "U.S.S.R."). The tension was so bad that every time Americans walked outside they halfway expected to see a mushroom in the sky, and Reagan did what he had to do in order to prevent it from happening. He was a commander in chief who was forced to spend whatever it took to keep Americans safe on domestic soil, and if he hadn't done it then we'd all be dead. Also, Iran was holding Americans hostage when he entered office. And Japan was taking market share away from the American auto industry and consumer electronics such as televisions, stereos and computers.
It seems to indicate that the U.S. economy has been in gradual, slow decline since at least 1980, with short term economic boosts such as the dot com and real estate booms, and the inevitable outcome was The Great Recession.