NEW YORK (TheStreet) -- A positive start to the week was short-lived as stocks fell into the red Monday after crude oil prices struggled to maintain a brief rebound.

The S&P 500 slid 0.37%, falling below the 2,000 level for the first time since Oct. 30. The Dow Jones Industrial Average fell 0.39%, and the Nasdaq was down 0.66%. The fresh declines come after the S&P 500 suffered its worst week in more than two years last week, falling 3.5%.

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Crude oil prices were falling again after secretary general of OPEC, Abdallah Salem el-Badri, said the oil cartel would not cut output even if oil falls below $40 a barrel. At last check, West Texas Intermediate was 1.2% lower to $57.14 a barrel. The International Energy Agency on Friday cut its forecast for oil demand in 2015 by 230,000 barrels a day to 900,000 barrels. It's the fifth time in six months the IEA has slashed its forecast.

"The much lower price environment for oil and other commodity prices will eventually cause equipment investment to slow in industries related to oil extraction, in our view," said Wells Fargo economists in a note. "However, we have maintained that [industrial] production would still hold up in the near term." 

Industrial production in the U.S. in November rose 1.3%, its largest increase in nine months, compared to an estimated 0.7% increase. October data on industrial production was upwardly revised to 0.1%.

China's central bank said Monday that its economy could slow to 7.1% next year compared to a forecast 7.4% this year, a result of its flagging property sector. Third-quarter GDP came in at 7.3%, a five-year low. China's Shanghai Composite was unperturbed, closing 0.52% higher.

PetSmart (PETM) shares spiked more than 4% on news it had agreed to be acquired by a group of private-equity investors led by BC Partners. The acquisition is valued at $8.7 billion, or $83 a share.

Oracle (ORCL) shares added 2.6% after Morgan Stanley analysts raised their rating on the stock to "overweight" on "low expectations and weak sentiment" heading into the company's earnings report on Wednesday.

Riverbed Technology (RVBD) climbed 8.5% on news it will be acquired by Thoma Bravo and the private-equity branch of the Ontario Teachers' Pension Plan for $3.6 billion, or $21 a share, a 12% premium to the tech company's Friday close.

Cirrus Logic (CRUS) surged 20% as Barclays upgraded the stock to "overweight" and more than doubled its price target to $28. The firm believes the company's chips will be increasingly used in current iPhones and future models of the Samsung Galaxy.

Talisman Energy (TLM) rocketed 19% higher after confirming discussions with Repsol, among others, for a potential transaction. Canada Pension Plan Investment Board is also exploring a bid, Bloomberg reported.

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-- Written by Keris Alison Lahiff in New York.

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