U.S. stocks ended a weak month on a mixed note Wednesday as the markets reopened following a two-day closure due to Hurricane Sandy.

The Dow Jones industrial average lost nearly 0.1%, while the S&P 500 ended flat. The Nasdaq lost 0.4%. For the month, the Dow fell 2.4%, the S&P 500 sank 1.9%, and the Nasdaq logged a 4.5% decline.

Many expected trading volume to spike Wednesday after Wall Street spent two unscheduled days in the dark. But the number of shares trading hands was held in check as many investors were still without power and transportation remained limited in New York City.

"There is some pent-up demand to trade after being closed for two days," said Art Hogan, managing director at Lazard Capital Markets. "But you have to balance that with the fact that many folks are still not able to get back to work."

The two-day trading halt was the longest weather-related closure of the NYSE since a massive blizzard struck New York in 1888. In a symbolic gesture, New York City mayor Michael Bloomberg rang the opening bell on Wednesday.

With the city's financial district without power, the stock exchange was running on gas-powered generators. The exchange was still working out some kinks, but it appeared to be functioning properly, said Lawrence Leibowitz, chief operating officer of the NYSE, in an interview with CNN.

"I think it's a symbol that makes everybody feel better -- that says we're back on our feet, we're open for business," Leibowitz said from the floor of the exchange.

Still, traders were reluctant to place big bets on the first day after such an unusual event. In addition, many investors are taking a cautious approach ahead of next week's presidential election and the economic threat posed by the looming fiscal cliff.

"A day like today, you just sit on your hands," said David Rovelli, managing director of U.S. equity trading at Canaccord Genuity.

Wednesday marks the end of the month and is the final day of the fiscal year for many institutional investors.

It's a day when many mutual fund managers will try to offset their capital gains with their losses to minimize distributions paid out to shareholders. However, some managers may have done their so-called "window dressing" last week in anticipation of the storm.

"This was a pretty well-advertised storm," said Hogan. "I think some of that work of closing the books might have been done last week."

Meanwhile, investors focused on companies that could benefit from the clean-up effort. Home improvement retailer Home Depot rose 2% and Lowe's gained 3%.

Shares of Great Lakes Dredge & Dock gained, along with Beacon Roofing and Owens Corning, which make insulation and building materials.

Shares of Generac, a generator maker, jumped 21% after the company boosted its earnings and revenue forecast for the year, as a result of "increased demand for home standby and portable generators" in the aftermath of Hurricane Sandy.

Insurance stocks, such as AIG, Allstate, and Hartford Financial were slightly lower.

Knight Capital stopped taking new trading orders Wednesday afternoon as it struggled with "power issues" and requested its clients re-route all stock orders to other trading firms, according to two traders who received a memo from the firm. Shares of the New Jersey-based broker-dealer fell 3%.

Related: Sandy clean-up will cost towns millions

Companies: Shares of Netflix surged 15% after activist investor Carl Ichan disclosed a nearly 10% stake in the online TV and movie rental company. In a regulatory filing, Ichan said Netflix may hold "significant strategic value" for larger competitors.

Shares of Facebook were down about 4% as many Facebook employees finally get a chance to sell their shares for the first time, after a lock-up on their so called "restricted stock units" expired. A total of 234 million Facebook shares will be newly eligible for sale.