My dell optiplex gx270desktop does not display but shows orange instead of green

Honestly? That computer is from 2004, I have an Dimension from 2003 that is almost just like it. In my opinion your computer is dead (bad motherboard, processor, or similarly expensive part that is cost prohibitive to fix). However, if you go to the Dell website you can look up the manual for it and there may be another explanation (like a dead hard drive, or bad ram). I'm sorry to be the bearer of bad news, but the good news is that a computer about like the one that you have can be bought off of Craigslist for around $50.