One of the first things I learned when troubleshooting SharePoint was to reset the SharePoint Timer Service Cache.
The basics of it are:
- Stop the SPtimerV4 service on a box
- navigate to c:\programdata\Microsoft\SharePoint\Config\someguid
- delete everything but Cache.ini
- edit Cache.ini and replace the number you see with the number 1
- start SPtimerV4
Nick Hobbs has done a very nice powershell script to automate this across your whole farm: http://nickhobbs.wordpress.com/2012/06/14/sharepoint-2010-powershell-to-clear-the-timer-job-cache/, based on a script from Mickey Jervin
Nice job Nick and Mickey!