When preparing taxes, you want to take every allowable deduction. Because you do not turn in any receipts with your tax return, you don't need receipts to claim the expense when you file.
If you don't have receipts, you may still claim expenses on your tax return without them. Other adequate records may include: cancelled check, credit or debit card statements, your written logs and records you kept during the year, calendar notations, and photographs.
Please note that if your computer is a necessary requirement for enrollment or attendance at an educational institution, the IRS deems it a qualifying expense. If you are using the computer simply out of convenience, it most likely does not qualify for a tax credit.