U.S. stocks picked up where they left off last week, extending a sharp selloff on Monday on worries over oil and disappointing earnings. Uncertainty over the Federal Reserve's rate hike plans also hurt sentiment ahead of Chair Yellen's testimony to Congress later in the week. Chesapeake Energy (CHK) was on watch after shares slumped to their lowest level since the turn of the century. Reports broke earlier that the company will undergo a massive overhaul of its operations and has already hired restructuring attorneys. Biotech firm BioCryst Pharmaceuticals (BCRX) tanked after reporting disappointing mid-stage study results for a highly anticipated drug. The treatment hoped to target a rare genetic condition that causes face swelling and restricts breathing. TheStreet's Keris Lahiff has details from Wall Street.