Dell Dimension E510 CPU Fan Problem

Does CPU fan work?

Did you gently clean top of CPU and bottom of heat sink and apply a thin coat of fresh thermal paste before you re-attached them? 

3-4 error code = Memory modules are detected, but a memory failure has occurred

2-4 error = Possible graphics card failure has occurred

Sounds like you didn't re-assemble correctly. Read the Service Manual for (re)installing components.

Start over by removing old motherboard battery and pressing/holding power button for ~30 sec. Next, apply fresh thermal paste between CPU and heat sink and re-attach. Then carefully re-seat all components in their slots. Last, install a fresh motherboard battery (CR2032 3-volt lithium ion battery, ~$2), close up and see if it boots now.

Re: I Went To Put It All Back Together and The CPU Fans Sounded Like a Literal Race Car! It Turned On and It Would Say Like "Previous Shutdown Due To Thermal Event" Then After Like 5-10 Seconds It Shuts Off.

Do not rely too much on diagnostic light code in this old model.  Your E510 has trouble doing POST (cpu fan at full blast without winding down).  Normally the fan goes full blast only briefly when powered up and quiets quickly (and often w a sweet short normal beep).  When POST is stuck (and not because cpu overheats right away), fan stays full blast.  Also even if you did forget apply thermal paste (which I doubt), the mere dry contact of properly mounted heatsink w cpu is still okay to provide some cooling and cpu temp would not rise precipitously, but slowly due to suboptimal thermal contact.

The BIOS may be in a dilapidated state living on a very old battery.  So do not trust much the screen message.  First thing to do is replace the old CMOs battery with a brand new one (if you had not done that).  Then try clear CMOs settings on motherboard by reset RTCRST jumper.

Reset the current CMOS settings:
a Locate the 3-pin CMOS jumper (RTCRST) on the system board (see "System Board Components" on page 67).
b Remove the jumper plug from pins 2 and 3.
c Place the jumper plug on pins 1 and 2 and wait approximately five seconds.
d Replace the jumper plug on pins 2 and 3.

P.116/142 https://downloads.dell.com/manuals/all-products/esuprt_desktop/esuprt_dimension_desktops/dimension-5150x_owner%27s%20manual_en-us.pdf#page116

@STOOPID216 

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You need to check the CPU heatsink mounting AND replace the CPU fan.

https://www.ebay.com/itm/224040355225

Dell E510 - HJ054

A better option would be to get an Optiplex GX620 tower or better an XPS 400 tower.

You can migrate EVERYTHING inside the E510 into the GX620 or XPS400 tower including RAM, CPU, Memory, HDD and it just works.

XPS 400 gives the added advantage of a full 8 gigs of Ram as well as upgraded power supply.

https://www.ebay.com/itm/324810132351

None of These Methods Worked and I Don't Know What To Do Now.

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@STOOPID216 wrote:

None of These Methods Worked and I Don't Know What To Do Now.

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Are you still getting thermal event errors or something else?

Yes I Am Getting Those Errors I Even Replaced the Thermal Paste and Changed The CMOS Battery