Reliability Monitor doesn't work in Win7 Ultimate

I suspect that the data collection is not enabled. Lets follow the steps below to enable it:
1. Enable Data Collection for Reliability Monitor
Reliability Monitor uses data provided by the RACAgent scheduled task. Reliability Monitor will start displaying a Stability Index rating and specific event information 24 hours after system installation.
The RACAgent scheduled task runs by default after the operating system is installed. If it is disabled, it must be enabled manually from the Task Scheduler snap-in for Microsoft Management Console (MMC).
Membership in the local Administrators group, or equivalent, is the minimum required to complete this procedure.
To enable the RACAgent scheduled task
   1.      Click Start, click in the Start Search box, type taskschd.msc, and then press ENTER.
   2.      In the navigation pane, expand Task Scheduler Library, expand Microsoft, expand Windows, and click RAC.
   3.      Right-click RAC, click View, and click Show Hidden Tasks.
   4.      Click RACAgent in the results pane.
      noteNote
      The RACAgent task name may not be completely visible. If you cannot locate it, expand the Name column in the results pane.
   5.      On the Action menu, click Enable.

If the above steps does not help
2. Reset Reliability Monitor:
1. Clear Your Windows 7 Problem Report History.
NOTE: This will need to do step 6 at that link above to delete all problems.
2. If Reliablity Monitor is open, then close it.
3. Open Folder Options and select (dot) the Show hidden files and folders option and click on OK.
4. Open Windows Explorer and navigate to C:\ProgramData\Microsoft\RAC.
5. To Backup this Reliabilty History Data -
WARNING: While this is an optional step, you will not be able to restore this data if you do not backup this data and it will be gone for good. If you want to skip this, then continue to step 6 instead.
A) Copy both the PublishedData and StateData folders and paste them to another location as a backup.
6. Open the PublishedData folder.
7. Select all the files in the folder and click on Delete.
8. Click on Yes to approve.
9. Open the StateData folder.
10. Select all the files in the folder and click on Delete
11. Click on Yes to approve.
12. If prompted by UAC, then you will need to click on Yes for each UAC prompt for each file in the StateData folder to approve deleting each file one by one.
13. Close Windows Explorer.
14. Empty the Recycle Bin.
15. Open Folder Options and select (dot) the Don't show hidden files and folders option and click on OK.
16. Open Reliablity Monitor to see it now reset clean.
NOTE: If Reliablity Monitor is already open, then close and reopen it.

For additional help you can also refer to the article below which explains more about the Reliability monitor:
http://technet.microsoft.com/en-us/library/dd744567%28WS.10%29.aspx

Hope it helps.