Strange reboot problem, please help me solve it

[trigger007]

OK im trying to overclock my core2 duo E6300 @ 1.86ghz to 2450ghz(350x7) with the standard cooling.

system specs:

intel core2 E6300
Gigabyte Ga-945p-s3 rev 1.00
Transcend 1024gb ddr2 667mhz X 2 (1.8V)
sapphire x1900xtx 512mb
160gb seagate sata
Thermaltake TR2-550 PSU

Current Bios Settings that works (v.F3):
CPU Host Frequency [338]
PCI Express Frequency [Auto]
System Memory Multiplier [2.00]
CPU Voltage [1.2000]

The Scenario:
I set my CPU Host Freqeuncy to 350 and System Memory Frequency to [2.00] (memory frequency is @ 700) and leave my CPU Voltage setting at [Normal], my pc boots up into XP, i then run various tests including "Toast", "Everest System Stress", "Orthos", "PCMark 2005 CPU", "3dmark2006",
"SuperPI 1M and 2M". It runs all the above tests without any problems at all, when i restart the pc its not booting and the screen stays black, i then switch off the system by pressing and holding the power button and then switch it back on and it boots again. I tried to set the PCI Express frequency to [100] but it reboots and cancels all overclock settings. I also raised the CPU voltage, but its still not booting when i restart, only boots if pc is switched off and then back on again.

If anyone can help me i'd appreciate it very much,
thanks.
Jacques

[Wizzard1]

Power supply might be a bit under-budget. Also, might want to up the vCPU a tad, unless thats right where you want it.