We will need a lot more information to help you with this if it is a genuine technical problem. I'll move this thread from Tech Sp to the Universe (gameplay) forum for now until we can better judge if it is a technical issue, a mod issue or a vanilla gameplay one (such as lack of trading softwares on your current ship or lack of weapon trade sources due to nil stock or poor reputation, etc).
Yeah, when you land, check to ensure that the station actually has something to sell you. Anything you can't buy is highlighted red if it's because of reputation. Try landing at the stations that make them, instead of the equipment docks.
If you're starting in the Argon Prime vicinity, there's a problem with getting basic Impulse Ray Emitter (IRE) laser weapons for your ship. There are NO IRE factories in the immediate area, so once they sell out (end of the first day), you can't find any in stock in the whole region. Particle Accellerator Cannons (PAC) require higher Reputation with the selling faction before they'll let you buy them.
As a first time player, I'd recommend either the Terran start (you get a ship with weapons), the Argon military start (better ship and guns than the Buster), or the Humble Trader start (unarmed Dicoverer and a Freighter, but if you can make a few thousand in a couple of good trades right away, you can get to an Equipment Dock with IREs before they sell out - if not, sell one of the ships and keep a few extra guns on the other). The first two starts will allow you to begin the main plotline almost immediately, which doubles as a tutorial to some extent, and hands you a bunch of steadily more powerful stuff as mission rewards. The Humble Trader start requires a bit of knowledge about the game to really make proper use of it, but gives you enough starting equipment to get you rolling without grinding cheezy missions for 50 credits until you can buy some new hardware or software. You can sell the freighter to buy some nice upgrades to the Discoverer (most importantly, Engine Tunings, better Sensors, and a pair of IREs and/or Mineral Scanner), then use the Disco to run missions properly, either station defense (the weak starting enemies can't really hurt a station, so you can only fail by dying) or asteroid mapping for steadily increasing amounts.
I agree with Honved. The 'custom' game is really meant as a base for modders creating new content. None of the plots are active, with one small exception, so you won't get a lot of the content of the 'normal' starts, let alone all the goodies that come from the various plots.
Have a great idea for the current or a future game? You can post it in the [L3+] Ideas forum.
X4 is a journey, not a destination. Have fun on your travels.