I urgently need to fit at least one but more probably 2 case fans. There is only 1 fan connection point on the MOBO. I should be able to fit a fan in the rear of the case and connect here.
There is a place to fit a fan next to the powere supply (which already has its own fan).
How can I connect that into the computer?
How would I connect it to the power supply. Is that safe to do and how? The only free 4 pin connectors seem to be set in a square and I suspect that the 4 pin connector on a fan might be set in a line.
Case fans can be powered either of two ways - 3-pin small connector to a mobo pinout, or a 4-pin Molex connector. (I am ignoring newer 4-pin small connectors for PWM fans, since this is an older mobo and machine.) That 4-pin Molex is the larger (about ¾" wide) one with 4 holes in a straight line that is on the end of wires from the PSU and usually supplies power to the back of an IDE hard drive. Very often there are more of these coming out of the PSU than you need and some are unused. BUT if your fan does not have the mating 4-pin connector on its wires (that is, it has the small 3-pin connector), you can get an adapter to convert from one connector to another. On the other hand, if you have NO spare 4-pin Molex connectors and need one (or more) you can get a different adapter that is a "Y" - it converts one Molex output from the PSU into two, thus creating an unused Molex. These Molex outputs certainly can supply enough power to add a couple of fans onto one output already in use.
Now, connecting a case fan to a Molex output means that it will always have full 12 VDC and thus run at full speed. You can buy controllers that fit between power supply and fan to reduce that speed to some other fixed setting if you wish.
If you want the mobo's BIOS to control your fans automatically (assuming the mobo actually can do this for any fan connected to it), you're going to have to get the fan plugged into the mobo SYS_FAN output pinout that is under such control. In OP's case there is only one such connector, already in use by a case fan. In these forums I have read that most mobo outputs like this actually can power TWO normal fans in parallel, but maybe not three. To do that you must modify fan wiring slightly. On a 3-pin fan connector the Black line is Ground, the Red line is the variable + VDC supply, and the Yellow is a speed pulse signal being sent by the fan back to the mobo. So you take two fans and, using the 3-pin connector already on the end of one fan's wires, you splice together the reds from both and then the blacks from both, but do NOT splice together the Yellows. Leave one yellow just not connected to anything. This will give you two case fans powered off one mobo output, and both will change their speeds according to what the mobo controller does.
OP, if you want a third fan, arrange to power it from a Molex. Let it run full speed always, or buy and install a speed reducer module for it. Either buy this fan with a Molex connector on its wires, or buy an adapter to make it work.
Ok, I have two fans in my box which are wired with 4-molex that has 2 wires intact, red and black. Mobo has a 3 pin place for fans power, so I quess I need to buy 4pin-topin adapter and connect to fans cables. Can I wire two fans in line with molex plugs and power with one wire from mobo?