suggest booting into Safe Mode and then using the run->eventvwr.msc to review
past events; look for errors in red first
eg:Event Type: Error
Event Source: Application Hang
Event Category: (101)
Event ID: 1002
Date: 7/2/2010
Time: 8:11:59 AM
User: N/A
Computer: LTBEARD
Description:
Hanging application helpctr.exe, version 5.1.2600.2180, hang module hungapp, version 0.0.0.0, hang address 0x00000000.
For more information, see Help and Support Center at
http://go.microsoft.com/fwlink/events.asp.
Data:
0000: 41 70 70 6c 69 63 61 74 Applicat
0008: 69 6f 6e 20 48 61 6e 67 ion Hang
0010: 20 20 68 65 6c 70 63 74 helpct
0018: 72 2e 65 78 65 20 35 2e r.exe 5.
0020: 31 2e 32 36 30 30 2e 32 1.2600.2
0028: 31 38 30 20 69 6e 20 68 180 in h
0030: 75 6e 67 61 70 70 20 30 ungapp 0
0038: 2e 30 2e 30 2e 30 20 61 .0.0.0 a
0040: 74 20 6f 66 66 73 65 74 t offset
0048: 20 30 30 30 30 30 30 30 0000000
0050: 30 0