SAN FRANCISCO (MarketWatch) -- Technology stocks continued to struggle in early trading Thursday, as a warning from networking-equipment maker Ciena Corp. highlighted the sector's negative action. Ciena shares fell $3.86, or more than 22%, to $13.54 after the company reported a large drop in its third-quarter profit and cut its fourth-quarter sales outlook. Other losses came from Cisco Systems Inc. , Microsoft Corp. and Hewlett-Packard Co. . The tech-heavy Nasdaq Composite Index fell 19 points to 2,314. ...