Is core duo e8400 compatable with ecs P965T-a motherboard. I cant get it to boot

the virtualisation capability is an option in the bios; that is where it can be anabled. To get into bios begin the boot up process and hit the delete button continuously. On some boards it is the F2 button but it should be the delete button on your board.
Remember to save the option on exiting.

I don't see the Gateway GT5238E motherboard supporting an Intel Core2 Duo E8400.....

The motherboard in the Gateway GT5238E has an Intel G965/Q963 motherboard chipset.
Front Side Bus, (FSB), support is 1066MegaHertz. (1066MHz)

ARK Intel G965 Express Chipset Intel 82G965 Graphics and Memory Controller


ARK Intel Q965 Express Chipset Intel 82Q965 Graphics and Memory Controller


The Intel Core2 Duo E8400 requires an FSB support of 1333MHz,


http://ark.intel.com/products/33910/Intel-Core2-Duo-Processor-E8400-%286M-Cache-3_00-GHz-1333-MHz-FSB%29


Gateway Motherboard GT5058j GT5238E GT5268E GT5436E 4006153R


(Scroll the page down)

JMHO

Regards,
joecoolvette

Press F1 or F2 or esc when trying to boot up to get into bios look for boot order choose dvd-rom as first boot device then drive0 you can change the order to boot from usb these days though i haven't owned a computer like that yet.

According to their website, no. The core 2 duo is supported, but not quad core. http://www.ecs.com.tw/ECSWebSite/Product/Product_Detail.aspx?DetailID=674&CategoryID=1&MenuID=16&LanID=0
Look under the cpu tab.

if you're not on a RAID, go try and remove it's cmos battery. then boot it up. shut it down then return the cmos battery.

Nope. because it only accepts AMD processors

Yes this motherboard supports PCIexpress card.
This is the link for the complete details of specs of this motherboard.

http://www.dealtime.com/xPF-Elitegroup-ECS-P965T-A-P965-P4-Pentium-D-Celeron-D-Core-2-Extreme-Duo-1066FSB-LGA775-DDR2-ATX-Motherboard-w-Au

Have you tried cleaning the RAM? Here's how it's done, remove the RAM from the DIMM slot of the motherboard and rub the pins with pencil eraser as shown in the image below:
then install again to the motherboard. Same goes with the graphics card (if you have one installed). if problems persist, replace the RAM..

your motherboard doesn't support this cpu. with the latest bios it will only support up to E6400. click here for more info.

http://www.ecs.com.tw/ECSWebSite/Products/ProductsDetail.aspx?detailid=681&CategoryID=1&DetailName=Bios&MenuID=44&LanID=0

personally i have the q6600 which is a quad core processor, all the others you listed were dual core, personally i use alot of programs all at once which is good if you have a quad core, but just for general music, data, and streaming, the e8400 is probably better for you, its a 3ghz processor.