My computer turns on but the screen is blank and the fans don't turn on besides the PSU fans.

Make sure that you actually installed the CPU correctly and make sure that all of your connections are securely inserted (such as the 4 or 8 pin CPU power cable) and make sure that the monitors VGA or DVI cable is securely plugged in

You could dissemble your memory, clean it and wait 30 sec and put it back in.
if it doesn't work try, the graphics card.
if that doesn't, then look here: http://www.tomshardware.com/answers/id-1722511/computer-starting-upgrading-cpu-motherboard-ram.html.
maybe you need a better PSU.

First I would say that if you can, take out the new CPU and insert the old CPU and see if the computer works as it did before you installed the new CPU

Then we can rule out if the new CPU is the issue and that it could be faulty or when you inserted it you could have accidentally bent one of the gold pins on the bottom of the CPU

Reply back when you've tried so that I can give you further instructions

I'm having the same problems. I had multiple CPUs so I tried another same results. NO FANS on CPU or CASE, but PS fans run, HDD spins. It's not the CPU because both work in another Gigabyte and MSI motherboard.

Someone said BIOS, maybe, but the FAN ISSUE puzzles me???

Looking for answers.

You should probably start your own thread and include your complete system specs. The same checklist I posted above can be used to troubleshoot your problem. It will help you figure out what's causing the problem if you perform every step in the checklist.

Shortstuff - we are both experiencing BIOS issues with the HP branded ASUS motherboard, P5LP-LE. Great Guide, and YES I have done all of that already, even checking the CPUs in other motherboards to confirm that they are indeed good. I suspect the other person has a good CPU as well.

I also ran into problem trying to use a late model video card even with an upgraded power supply. None of the ATI Radeon 5/6/7xxx series will work due to BIOS compatibility issues. I did find that the older Nvidia Quadro NVS2xx series to offer some performance gains over the stock video and did not seem to suffer BIOS problems while adding dual display functionality.

The CPU issue that we are both experiencing is due to the BIOS, not the board, being able to support newer video and CPUs. Some of the newer m7xxx series were Core2 Duo with the same motherboard, but I am assuming a different BIOS (same case, also LGA775, different model). The only thing I can tell is that the BIOS is a later update.

However flashing that BIOS to the P5LP-LE could brick the board because of some funky things that HP does to prevent such attempts. Like the OEM restore media will fail reporting that it's not for that machine build because the BIOS was changed, code PURPLE on boot, requires an HP utility to fix and authorize the BIOS version update. I'm expecting flashing newer BIOS will do the same. Was hoping to keep it semi-officially an HP box without all the upgrade drama just swapping the CPU.

Since these machines are essentially abandoned by HP for newer hardware and because Windows Media Center (XP) was the OEM supplied OS and is now discontinued by Microsoft it's a hands off "we don't do that anymore" situation when looking for updates and support either from HP or Microsoft.

Since I have two identical machines I'm willing to risk flashing one to find a solution that can update both for video and CPU updates. One is running Windows 8 Pro and the other Windows 7 Ultimate, neither supported officially. Both still have the original D820 2.8 Ghz CPUs currently and like I stated before have outlived many other newer computer purchases, rock solid reliable... Only items that ever went officially bad was one DVD/RW Light Scribe drive in 8+ years