Very strange: First boot always freezes, then a hard reboot fixes it.

[PHOENIX55B]

Recently my computer started doing random restarts. HDD was clicking, so I replaced the HDD and did a reformat and reinstall. After a few days the first boot of the day freezes about five minutes of being on. The keyboard and mouse go dark and I must do a hard restart. After that, the computer seems to work fine. I have ran the Dell Diagnostics and it shows everything is good. I have also tried several after market software and hardware checkers all showing all is well.
Windows 7 with all updates installed.
Dell XPS9100 with 9gb of RAM.
Upgraded Corsair 750 watt PSU
Upgraded nVidia GTX 470.
Upgraded WD Caviar 1tb HDD's (2)
Intel i7 2.94
Don't know the brand of the MOBO or memory. I suppose it's some default make that Dell uses.
Dell replaced the MOBO, Memory and CPU about a year ago under warranty due to constant BSOD's.

 

[PHOENIX55B]

Got it fixed. The line to the power button was loose. Must have tugged the wire while replacing the hard drive or while cleaning out the dust.