This is the first time I'm posting question here, hope I will be able to get some help

Here is my problem. Sometimes, the user will report that the Consolidated value is not computing, for example, in the month dimension, Q1 consists of child Jan, Feb and Mar. In Jan, value = 100, Feb value = 200, Mar value = 300. Q1 should be reflecting 600, by consolidating these figures, but the Q1 is only reflecting 300. When I click on the Check Calculated Calculation, I can see the row Mar value is showing 0. When I double-click on Mar(Mar is a computed field), then I can see 300.
After we did a server reset (due to other reason), this issue is auto fixed. The consolidated figure is now computed correctly.
This issue had been haunting us. We are using IBM Cognos Express Xcelerator Version 9.0, Windows server 2003, 8Gb RAM.
What could have cause the consolidated amt not consolidating (sometimes)?
Please share with me your views on this.
Thank you

Cheers.