When my Games For Windows Marketplace Client would not start I found that installing Windows Live Essentials fixed the problem.
The Error I was getting:
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Problem Event Name: CLR20r3
Problem Signature 01: gfwlclient.exe
Problem Signature 02: 1.0.0.0
Problem Signature 03: 4d93c2a6
Problem Signature 04: XLiveServices
Problem Signature 05: 1.0.0.0
Problem Signature 06: 4d93c2a5
Problem Signature 07: 5bb
Problem Signature 08: 4d3
Problem Signature 09: System.EntryPointNotFound
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