Optiplex 755

OPEN GL in the context of what you want requires a Video Card.

There are Various Sizes

MT (Mini Tower)
DT (Desktop)
MFF (Micro Form Factor)
SFF (Small Form Factor)
USFF (Ultra Small Form Factor)

AIO (All in one)

Fortunately there is a solution that works with ALL 755 models EXCEPT FOR USFF.

https://www.dell.com/en-us/work/shop/msi-gt-1030-2g-lp-oc-graphic-card-2-gb-gddr5-pcie-30-x16-low-profile-hdmi-displayport/apd/aa362018/graphic-video-cards

https://www.youtube.com/watch?v=2y32mBdZHJY

the answer is no.

only like 5 games run OPENGL ,

is this your only game?  is it Warcraft for Doom 2016? IDK

why not say purse size, first. I have x to spend,  otherwise other solutions  can not be told.

like a tad newer PC.

go back to w7 and hope intel support fixes this? your PC has w7 support. not 10.

are you using old Warcraft 3 that can run opengl  or  and DX

doing this?  year 2010 done long long ago.... this?

"C:\Program Files\Warcraft III\Warcraft III.exe" -opengl

tell what you want to run.

755 is old , and no case size told as we beg endless here, and nobody reads.

755 MT, DT< SFF or >?

DID YOU READ YOUR DELL 755 SUPPORT PAGE ON DRIVERS FIRST? NO , AS support ended at VISTA

I guess you have no PCI-e GPU card , the w10 driver or the iGPU onboard is weak.

this PC has CORE2 DUO in 11 of 13 versions

and with INTEL, HD 3100 ON BOARD CHIP GPU.

INTEL HAS NO REAL SUPPORT FOR THIS CHIP NOW, W10

Intel says NO.  ended at w8

so buy GPU card ,

NO PC stated so no possible answers, accurate.  no APPS stated, gaming, name one game that runs slow  now. (all sure) but not naming one of 10000 games sold , makes answers IMPOSSIBLE.

I have old PC, and dream to run X, name X

please.

the chips Intel made for HD or GMA graphics legacy  are all listed here,  this is all you need to know about the 

onboard chip.

all support ended there in 2016 June.  RIP 3100

if you looked in device manager the GPU chip there tells you its a lame version from MS,  marked as.

with MBDA  (and poor resolutions and SLOW

if you see that ever there that means its  LIMPHOME MS driver, "just barely works" driver, ending black dead screens when updated to w10,  MS did that magic.

buy a card,

did you know both AMD.com and Nvidia;com both list all cards that are supported in W10 for sure

Additional info:

Optiplex 755 Tech Guide 

the answer is NO.

 "without having to buy a graphics card"   so the endless 1030 slam dunk $80 cure on this forum fails.

simple and for a fact intel.com ended your support on your ONBOARD GPU. (but not for w7)

but no game told so no magic tricks possible here,  why not tell what fails first and ask for solutions all.

name a game, is that too hard, then buy a newer PC,  dell 3020MT is best for low $50 cost used, and prime.

I have turing class GPU card in mine but was not cheap so.... no help to you.

there are 2 path here,  some games can be had that do not use OPENGL.

in fact only a few games use that, most use DirectX  (vast) and version matter too,  gaming.

doom 2016 , Minecraft, and these?

the Directx list by version is here, so you can pick a game that runs on dirty cheap and older GPU  cards.

that be first thing to learn on games lacking Bread (gold dust)

DX11

DX 10

The older the game you might like the cheaper the GPU will be , if running w10 (I bet not) but are, then see all cards from my simple list here ,

in those lists,  you see older card there that work with w10 those are cheaper cards and if you buy one a game will run , and even run better on a slow PC if you adjust the game as the (unknown ) game forum for it directs you.

do  tell more. we can work many angles to gaming,  sure can.

The best post would be, I need to run x,y,z 3 games, what is the lowest cost path to doing that.

and what OS your run or would like to run.

if minimum FPS is needed say so. 

now lets work that angle. (low buck cures)

let me pick a card, solution that is not expensive, called USED GPU Cards (vast but is simple)

NVIDIA support series 7 cards up in W10 , now. pick one, buy one.

GTX705 to 780 are the oldest supported cards, that game by maker. (3D optimized) 750 cost $50 used.

GT705 are . $20 but rare,  710 $25,  730, $26 and climbs to 750- price, slower to faster , you pay the price.,

now AMD oldest and cheapest used DX11

AMD Radeon™ HD 5000 Series/AMD Mobility Radeon™ HD 5000 Series Graphics

AMD Radeon HD 5450 - PCI\VEN_1002&DEV_6779&SUBSYS_30081787   ( $8 too much????)DVI !?
AMD Radeon HD 5450 - PCI\VEN_1002&DEV_6779&SUBSYS_A007174B
AMD Radeon HD 5450 - PCI\VEN_1002&DEV_68E4&SUBSYS_5450174B
AMD Radeon HD 5450 - PCI\VEN_1002&DEV_68E5&SUBSYS_E164174B
AMD Radeon HD 5450 - PCI\VEN_1002&DEV_68F9
AMD Radeon HD 5500 Series - PCI\VEN_1002&DEV_675F
AMD Radeon HD 5500 Series - PCI\VEN_1002&DEV_68DA
AMD Radeon HD 5570 - PCI\VEN_1002&DEV_6742&SUBSYS_55701458
AMD Radeon HD 5570 - PCI\VEN_1002&DEV_6742&SUBSYS_5570148C
AMD Radeon HD 5570 - PCI\VEN_1002&DEV_6742&SUBSYS_5570174B
AMD Radeon HD 5570 - PCI\VEN_1002&DEV_6742&SUBSYS_55701787
AMD Radeon HD 5570 - PCI\VEN_1002&DEV_68C7&SUBSYS_5570174B
AMD Radeon HD 5570 - PCI\VEN_1002&DEV_68D9
AMD Radeon HD 5600/5700 - PCI\VEN_1002&DEV_68B9
AMD Radeon HD 5670 - PCI\VEN_1002&DEV_68D8
AMD Radeon HD 5700 Series - PCI\VEN_1002&DEV_68B8
AMD Radeon HD 5700 Series - PCI\VEN_1002&DEV_68BE
AMD Radeon HD 5800 Series - PCI\VEN_1002&DEV_6898
AMD Radeon HD 5800 Series - PCI\VEN_1002&DEV_6899
AMD Radeon HD 5800 Series - PCI\VEN_1002&DEV_689E
AMD Radeon HD 5900 Series - PCI\VEN_1002&DEV_689C

5450 support is here w10 with Directx 11  !

here is your lowest cost solutions, examples, surely 8 buck is better than $80 GT1030, for low buck fix.

Is this 5450 not the BINGO winner in lowest card w10 that runs lots of games,  YES.

All models EXCEPT Micro USFF and AIO can use Low profile 40W GT1030.

Mini tower with 300W power supply or more can use 1050TI. which is as good as the GTX680 from 2012

So 2 gig or more Video ram and Directx 12 is better than older cards and works with most current games.

A major limitation is the size of the PC and the size of the video slot. So only short cards work.

Pascal based cards work better and use less power than previous GTX 660 680 750TI  Kepler based cards.

https://www.youtube.com/watch?v=wEs9dyS9e-Q

https://www.youtube.com/watch?v=BUOrnp2PjK4

https://www.dell.com/en-us/work/shop/msi-gt-1030-2g-lp-oc-graphic-card-2-gb-gddr5-pcie-30-x16-low-profile-hdmi-displayport/apd/aa362018/graphic-video-cards

The pascal based 1030 is a good option for most older models including GX620 tower , Precision 380 Tower, XPS400 Tower from 2006 which is 13 years old now.

Up to and including 1080 TI is possible with older dell if it fits into the case and you upgrade the power supply.

https://www.youtube.com/watch?v=mHTMZHcFaJE

https://www.youtube.com/watch?v=-mLDlrLQZXs

https://www.youtube.com/watch?v=qa9b0TkTsLM