Summing Multiple Rows In Columns

I am working with a MS SQL database associated with SCCM 2007. SCCM collects software product usage data, and I am tasked with generating a report that will return results between two user-chosen date ranges. I set up prompts for month, year, endmonth, endyear. They would enter 2, 2014, 4, 2014 for example. Timekey would equal 201402, endtimekey = 201404. The tables I am concerned about look like this:

v_MonthlyUsageSummary

TimeKey ResourceID FileID UserID UsageCount TSUsageCount UsageTime LastUsage
201402108343 253362240038122 0 2550272014-02-28 13:29:39.000
201402108340 253362240665 2 0 122014-02-27 15:58:13.000
201402108932 253362231708 0 10 216702014-02-14 20:41:35.000
201403124035 504006542145 15 0 1756292014-03-31 19:37:37.000
201403124036 504006537579 46 0 7737112014-04-01 00:00:00.000

v_SummarizationInterval

TimeKey IntervalStart
2013102013-10-01 00:00:00.000
2013112013-11-01 00:00:00.000
2013122013-12-01 00:00:00.000
2014012014-01-01 00:00:00.000
2014022014-02-01 00:00:00.000
2014032014-03-01 00:00:00.000
2014042014-04-01 00:00:00.000
2014052014-05-01 00:00:00.000
2014062014-06-01 00:00:00.000
2014072014-07-01 00:00:00.000

The problem is I only know how to grab one timekey, but I need to combine multiple timekeys to sum up the usage counts for each workstation.

Here is the full query.

declare @TimeKey int
declare @months float
declare @endTimeKey int
set @TimeKey=100*@Year+@Month
set @endTimeKey=100*@endYear+@EndMonth
select @months=DATEDIFF(d,@timekey,@endTimeKey)

[Code] .....