Something strange happened in the tech sector in May. Without a clear sell signal, tech stocks seemed to slip into some kind of investor oblivion. Exhibit A, of course, is the Facebook (FB) IPO, which in its first trading days has lost a quarter of the value that Wall Street’s supposedly smartest underwriters thought it was worth. Facebook has pulled down other recent web IPOs as well: Groupon (GRPN) is down 15% since Facebook listed and Zynga (ZNGA), which relies in good part on Facebook for revenue, is down 29%.

But overlooked in all the coverage about the cold shoulder investors have given to recent web IPOs is the slump that good old-fashioned, blue-chip tech giants have faced. As bad as Facebook has fared since its IPO, old-line tech brands like Dell (DELL) and Cisco (CSCO) have fared just as poorly this month. Meanwhile, others big-name tech stalwarts have also declined unexpectedly. And there’s no single piece of bad news to explain it. It’s just that investors seem to be weary of tech as a growth sector.

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As of Tuesday, the Nasdaq Composite is down 7% so far in May. Many large-cap stocks have fared much worse. Dell is down 23%, Cisco is down 19%, and Oracle (ORCL) is down 11%. Hewlett-Packard (HPQ), Microsoft (MSFT) and Intel (INTC) have all dropped 8%. IBM (IBM) is among the few tech giants that has outperformed the Nasdaq, falling a mere 6%.

Of course, there is always a risk in extrapolating too much from a single month of stock trading, especially one that faced economic uncertainty in nearly every part of the world. But it used to be these same blue-chip tech names were seen as safe havens when other sectors were declining. Now, investors are inclined to sell tech when the broader market faces uncertainty.

What gives? The biggest culprit seems to be a broad-based slowdown in the pace of spending on information technology, thanks to financial turmoil in Europe and a stronger dollar. Global IT spending by companies and governments is expected to total $3.75 trillion this year, according to research firm Gartner. But Gartner recently lowered its forecast for the pace of spending. Instead of expecting a 3.7% growth this year, the firm now expects IT spending to rise by only 2.5%. Last year, IT spending grew by 6.8% as companies straightened themselves out after the 2008 crisis.

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Some sectors are likely to fare better than others. Telecom equipment spending is expected to rise by 6.9%, close to the 2011 rate. Spending will rise 5% for enterprise software and 4.3% for computing hardware, both down significantly from last year. Telecom and IT services, however, are expected to grow by about 1%, well below the 6% rate for 2011.

That slower growth is coming at a time of disruptive change in many areas. Cloud computing is forcing enterprise-software giants like Oracle to rethink their old ways. (CEO Larry Ellison, after years of bashing the cloud, said Wednesday he’s learning to love it.) Cisco’s stock tumbled this month not just on concerns in Europe, but on the rise of Asian competitors like Huawei, which made its CEO sound rather defensive on its recent earnings call with investors.

And mobile computing is eating away at the stronghold that PCs made by Dell and HP had in the corporate market for many years. A Barclays Capital analyst said Wednesday that Apple (AAPL) iPads and iPhones may be “used for more PC tasks, elongating buying cycles and replacing some PCs altogether.”

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Then there are the turnarounds that some of these companies are stuck trying to pull off: HP’s aggressive layoffs, Dell’s push away from PC sales and into IT services, Cisco’s effort to find a strong second act. Many investors lack the patience needed to stick with a big company’s turnaround, and its inevitable setbacks and false signals.

So despite the low PE’s on blue-chip tech — HP’s is 6 for the next year, Dell’s is 5, Cisco’s is 8 — investors just aren’t buying the story that large-cap tech companies are turning themselves around. Some of the biggest success stories of the tech sector are now some of the hardest sells on Wall Street, even though they are profitable and showing modest if steady growth.

The blue chips of Silicon Valley have gone, in the last decade, from the growth stocks everyone wanted to the value stocks few value investors would touch. And that makes these blue-chip stocks very blue indeed.

Kevin Kelleher is a writer in the San Francisco Bay Area. You could find growth and value – or most likely, neither – by following him on Twitter.