Your VGA card or port may have been possibly damaged, I'm thinking. But before that please follow Shine's comment and also see this link as well.
https://dell.to/3P7b9wJ

Monitors are hot pluggable to PowerEdge server. Did you have any GPU installed on the server? I am suspecting your server have local video disabled on iDRAC. As you do not have access to iDRAC it will be difficult to check that status.

Did you have remote access (Remote Desktop or SSH) to current operating system installed on the server. If yes and operating system is supported you can install iDRAC Tools and reset iDRAC root password. 

If server is ordered with non default iDRAC Password then iDRAC password will be available in information tag of the server. You can refer below link for details

https://www.dell.com/support/kbdoc/en-us/000133536/dell-poweredge-what-is-the-default-username-and-password-for-idrac 

This solved my problem. Video need to be

checked in the idrac settings...

I found that the video checkbox MUST be selected to get VGA video to the monitor.

I have PowerEdge R640 and when I power on it, the fan speed is high and the cooling is very high. Moreover, it shows  multicolor vertical bands VGA display only and unable to detect mouse and keyboard.

Please let me get a solution to these problems

Hello,

it sounds that motherboard has some issue.

I suggest you to follow this article to troubleshoot the issue

PowerEdge: Troubleshooting a Server that Does Not Start (No Power, No POST, No Boot and No Video) | Dell US

Thanks

@DELL-Marco B​ 

Thank you for your suggestions. However, both No Video and No POST troblshotting are not working for my case. FYI, the problem is happened after my friend tries to configure the server for some data management. Do you think something related to iDRAC? If that might be the case, please guide me how to access iDRAC for my case.

Hello,

I need some info to understand.

When you power on the server onsite, there something appears on the screen? Or there is no video?

If there is no video I suggest removing all devices and power on the server with only minimum to post:

• One processor (CPU) in socket processor 1
• One memory module (DIMM) in socket A1
• One power supply unit
• System board + LOM card + RIO card

Thanks

When  I power on the server onsite, the cooling fans spinning at full speed and the screen display vertical multiple color bars as shown below. 

Thank you

Hello,

for me the issue is coming from the motherboard, that probably it is faulty.

Thanks