9020, power button LED, amber blinking

And Also Why Were The Lights Blinking, Now It's Working Fine But I Am Still Concerned. It Is Also Not Overheating.

There's different models of the GTX 750Ti 2GB - EVGA, Nvidia, Zotac, etc.  I looked up a couple of them and they're 60w.  Your PCi-e slot gives you 75 watts.  I don't think the hiccup was GPU related.

I do think the hiccup happened when your Ethernet card burnt.  It probably shorted itself out.  Does it actually still work?  Either way, you're probably safer getting a new one.

One thing Dell regularly recommends when errors happen is disconnect peripherals first and see if the error continues.  With your computer working, I don't consider it necessary.  But again, I think it was your Ethernet card.

Edit:  Well, in one post you said "Ethernet adapter" and in another "Ethernet cable adapter."  Either way, if it burnt, it probably shorted and should be replaced.

Well No My Ethernet Cable Adapter(A Rectangular shaped Thing Which Is Inside PC) Is Not working Anymore, I Used To Use It But I am Now Unable To And Also When I Check The Adapter It Gives Me An Error Saying

"This device cannot start. (Code 10) {Operation Failed} The requested operation was unsuccessful.

Btw I Have Nvidia GTX 750ti 2GB

And No It(Ethernet Net Adapter) Was Burnt Several Months Ago And I Ran Into Trouble With BLinking Amber Lights Days Ago.

Ok So Last Thing I Want To Know Is That Should I Change My PSU With A Better One?? Like 400 Watt Or More? 

Will It Work Well?

Your 290W PSU is just fine for your GPU.  Even if you went thru the trouble of upgrading PSU's and wanted to use a higher watt GPU, you'd still have to use low profile single slot cards with their own power cable.  I think your setup is just fine as long as your happy with your GPU.

If your still curious about optional PSU's, "9020 MT PSU" can be used for a search term in Dell Community and you could Google it as well.  Chances are optional PSU's for the 9020 was already answered.  @speedstep is an expert at it.

Right, I Want To Replace My GPU With A Better One. But I Don't Understand Why Do I Still Have TO Use Low Profile GPU With Their Own Power Cable?? Power Cable? There Is Only One Power Cable Which Is Of PSU. I Don't Understand Very Well, Why DO I Still Have To Use Low Profile GPU Even When I Upgrade My GPU?

I Am Look TO Replace Gtx 750ti With Gtx 1050Ti 4GB Or Rx 560 4 GB

What Should i Do Than?

Because space is limited and you only have one PCI-e x16 slot.

I gave the wrong impression with the power cable.  The impression I meant was if you upgrade GPU's, power will have to plugged into it.  It can't draw all of its power from the MB.  Remember, and I think you know, if you upgrade GPU's, you'd have to upgrade PSU's.  I'm not 100% sure what there will be for cables then. 

I'm not the best expert at GPU's.  I don't mind if one of our Rockstars or other experts chime in.  That would probably be best if you have anything further in regards to PSU's and GPU's.  I'm sure you'll want the best matchup.

It's Alright I Will Search For It But Today The Amberlights Problem Came Back It Was Same As Before. Blink..Blink......Blink I Used The Same Method That I Used Before To Fix It. It Was Holding Power Button For 7-9 Seconds And Then Pressing Power Button Twice It Again Fixed It But I Don't Still Really Understand What Would Cause It To Come Back?

Back up everything you want backed up - files, music, videos, etc.  You can also make a full backup image of OS and files using Macrium Reflect.  One of our Rockstars likes that one.  A full backup image to flash drive will take a while.  It's also built into Win10.  I don't remember if Win7 has it.

I immediately jumped to backup in case your computer completely goes out.

It wasn't mentioned - I take it your burnt Ethernet is disconnected?  If so, you might be due for a newer computer.  That might work out best since you wanted to upgrade GPU's and have a machine that powers it.  Remember, that blink pattern, according to Dell's diagnostics, is indicative of an MB problem.  A problem might just be starting and get worse over time.

That's the best answer I can give you.  It's impossible to run complete diagnostics from here.  A computer shop would have to do that.  It might not be worth sticking money into that PC anymore, but that's entirely up to you.

There's a way you can run diagnostics - At startup, at the Dell splash screen, use F12 for the Boot Menu.  Arrow down to Diagnostics and hit enter.  Fyi - It'll take a while.  Please post any error msgs. or take a photo of your screen in the event of error message(s).