I confirm the processor-board-memory-hard drive combination you mentioned should be a fine one for the Intel(R) Desktop Board DP35DP. However, would you mind providing more details?:
1. How slow is "slow"?
2. At what point, during operation, does the system run slowly?
3. What program(s) are you running?
4. Are you receiving an error message? If so, please provide the exact wording of the error message.
5. Is there any conflict shown in Device Manager? If so, please, provide details on it.