The answer provided by JulieS is incorrect. Your Roth IRA contribution is in no way limited to MAGI. Yes, you can contribute to a Roth IRA. The amount of compensation reported in box 1 of the W-2 supports a Roth IRA contribution regardless of any Schedule C loss. Upon entering a Roth IRA contribution into TurboTax, TurboTax will not flag the Roth IRA contribution as an excess contribution (provided that your MAGI for the purpose is not so high that the amount that you are eligible to contribute to a Roth IRA is limited.
See IRS Pub 590-A page 6, "What is Compensation?" where it says that the amount in box 1 of your W-2 minus any amount in box 11 is supporting compensation.
