Jan 25 (Reuters) - The Nasdaq opened at a record high on Monday as markets geared up for a busy week of earnings from mega-cap technology firms, while the Dow and S&P 500 came under pressure from a decline in Merck’s shares. The Dow Jones Industrial Average fell 7.1 points, or 0.02%, at the open to 30989.85. The S&P 500 rose 10.2 points, or 0.27%, at the open to 3851.68, while the Nasdaq Composite rose 138.1 points, or 1.02%, to 13681.211 at the opening bell. (Reporting by Devik Jain in Bengaluru; Editing by Shounak Dasgupta)