ADGC said:

I have an Acer Veriton Z4620G that is not booting up when the power is turned on.  The on button LED does not light. The cooling fan starts and stops after three seconds. I cleared  the CMOS using the motherboard Jumpers and still no change. It originally carried the Pentium G645 processor and was upgraded to the intel Core i7-3770S 3.1GHz Quad-Core processor and worked great for a few days.  When it stopped booting up I returned to the G645 processor but the problem remains. I suspect its the BIOS is corrupted.  I recently replaced the MotherBoard that had the exact same problem.  Any help would be appreciated.

Firstly, your "OEM Acer Veriton Z4620G mobo has the Intel H61 Express Chipset and as your AIO OEM comes with the Intel G645 Sandy Bridge Socket 1155 CPU ( I would have upgraded the CPU to the Core i7-2700K as that would have been more compatible and given you 150% more performance to your OEM G645 as it would be more compatible) as Acer's highest spec in the Acer Veriton Z4620G AIO OEM CPU's is the Intel Core i5-3330S QC 2.8G 6M 65W Ivy Bridge Socket 1155 CPU" (the upgrade list for these 3rd Gen CPU's like the i7-3770S does not have your Intel G645 CPU on that list to upgrade from to the i7-3770S) as the i7-3770S is the highest spec 3rd Gen CPU socket 1151 and is probably not compatible with your mobo and Intel H61 chipset, yes it might have worked but it could have done some serious damaged to your mobo (burned out capacitors etc, have a technician inspect your mobo) as you could be going around in circles as this could have done some damage to the circuitry of your mobo and doing anything else could be useless. There are allot of variables to what you can upgrade a CPU and system to. These are the Acer OEM CPU's that your AIO Acer Veriton Z4620G mobo was fitted with OEM that work 100% and its memory and graphics specs also:

CPU's

• Intel Core i5 3330S QC 2.8G 6M 65W 
• Intel Core i3-2120 3.30G 3M 65W 
• Intel Pentium DC G630 2.7G 3M 65W 
• Intel Celeron DC G530 2.4G 2M 65W

Memory 

• Socket Type: SO-DDR-3 connector 
• Socket Quantity: 2 DIMMs - 
• Channel A: 1 slot; Channel B: 1 slot
• Dual channel support
• Speed support:DDR-3 -1333MHz
• Capacity support: SO-DDR-3 un-buffered non-ECC DIMM support - 1GB to 8GB max. memory support
• Design Criteria: - Should meet Intel Chipset platform design guide - Dual channel should be enabled always when plug-in 2 same memory size DDR-3  memory module - Should meet Intel chipsets family BIOS specification.

Graphics 

Intel HD Graphics technology (Microsoft DirectX 10) 

Discrete graphic cards supported (Microsoft DirectX 11)

• NVIDIA GeForce GT 530
• NVIDIA GeForce GT 520

Now with the pre boot, do you get any “Beep Codes”(see bewlo)??? As you should get some of these below, which ones are you getting??? As they are used by the BIOS to indicate a serious or fatal error to the end user. Beep codes are used when an error occurs before the system video has been initialized. Beep codes will be generated by the system board speaker, commonly referred to as the PC speaker. AMIBIOS displays the checkpoints in the bottom right corner of the screen during POST. This display method is limited, since it only displays checkpoints that occur after the video card has been activated. Not all computers using AMIBIOS enable this feature. In most cases, a checkpoint card is the best tool for viewing AMIBIOS checkpoints. 

Also you could have problems with components that could be affecting and causing your problems, like the new mobo (might not be the correct mobo?) your graphics and its drivers, your spinner HDD could be damaged (bearings or heads of the HDD) your RAM could be damaged and your power supply and cables, so systematically diagnose all these components to see if there are any problems. Give us more details as what you are describing could be numerous problems, good luck and hope this helps. 

Acer Veriton Z4620G Beep Codes