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is another haloce.exe or halo.exe running at the same time as you starting up halo?
if so, end that process, because it is using the same resources as the halo you want started up.

if not, try doing a clean startup (ie. no background programs running when you start up your comp) and try running halo again.

if even that can't work, scan your comp for viruses using UPDATED antivirus and antimalware software (like AVG or Malwarebytes).

last but not least, reinstall halo ce if all else fails.