The DHCP service would not seem to be something that would freeze your system. Have you tried disabling the Network adapters to see if the problem continues? If it doesn't, perhaps get a new driver for the adapter.
If DHCP is actually involved, something might have corrupted it. If you can, open an administrative command prompt and type SFC /scannow to check your system files. Let it run and report back if it shows any files it cannot repair.
If opening the start menu freezes things, you might be able to use explorer to go to the C:\Windows\System32 folder and right click cmd.exe and select "Run as Admin".