The Market Opens 4% Lower On Monday Than It Closed On Friday

One possible cause for the collapse of the NASDAQ (and all dotcoms that collapsed) was the massive, multi-billion dollar sell orders for major bellwether high tech stocks (Cisco, IBM, Dell, etc.) that happened by chance to be processed simultaneously on the Monday morning following the March 10 weekend. This selling resulted in the NASDAQ opening roughly four percentage points lower on Monday March 13 from 5,038 to 4,879—the greatest percentage 'pre-market' selloff for the entire year.

http://en.wikipedia.org/wiki/Dot_com_bubble