I just installed a gig of RAM in my computer, making it 1.25 Gib, is my computer reading it?

In a word, "No"

You need to be sure your mobo supports what you put in it. During POST, is the memory being counted? (I don't think so). You could try swapping the two sticks into the other's slots. Perhaps slot is dirty. Maybe not inserted fully? You can also try booting with just the 1gig of RAM (some boards would prefer one stick in Bank 0). It likely won't boot but maybe you are just over your limit (many boards top out at a gig) But could be the memory isn't supported by your mobo or is defective. You want to share specs on your machine and the memory?

Apparently it only reads it when there is only the 1gig installed. Oh well, its a lot faster.

1 gig does top out a lot of boards. Save the other stick. Doesn't hurt to have a spare lying around.

If your system is an HP Pavilion a1410y, the maximum memory that Crucial saids is 2 GB. Each memory slot can only handle 1 GB memory module.

A few causes that makes systems can not detect the new memory are the following.
1) New memory module is not firmly pressed down.
2) Dust is obstructing the contact of the new memory module.
3) The unused memory bank could be broken when new memory is inserted.
4) The power cord was still connected to the AC outlet and the standby current that is running through the system may have glitched some components. It is best to have the computer completely off and disconnected from the outlet.
5) The BIOS may need to be reset to take the new installed memory.
6) Some systems may require interaction during boot up to take advantage of the new installed memory.
7) memory module is not compatible with the present memory module and/or with the system.

8) if the mainboard is fairtly new and support Dual Channel DDR then that second slot is ignored unless it matches the first slot.

Does not matter if the motherboard is new. It matters of the chipset or the processor containing the memory controller that supports dual-channel. Intel chipsets and previous dual-channel memory chipsets do not require the user to use equal memory capacity and speed. These types of chipsets are flexible while some K8 processors are not. Number 8 will be like.
8) The processor containing a memory controller such as K8 that requires pairs of memory modules to be same the speed and capacity.

More are as follows.
9) When using RAMBUS memory, all banks have to be in use. The module can either be RIMM or CIMM.
10) Using a memory module containing higher density chips than what the memory controller supports.
11) Some chipsets or memory controllers that has dual-channel support will need to use single sided memory modules. These types of memory modules have chips mounted on one side instead of both sides.
12) When a motherboard contains three or more slots, use only two double sided memory modules, but only if it does not interfere with 11.

Some BIOSes require you to actually go into the BIOS setup, do anything or nothing, and then save the configuration before it will recognize new memory. I have no idea whether this is what's happening or not, though.

The point is it the mainboard is fairly new generation
there is very high chance that the 2 dimms were designed to be purely a Dual Channel Array

as your aware if you have 4 dimms
with
A A - B B
each matching letter is Dual Channel Array
AA must have only 1 or two matching sticks
BB must have only 1 or two matching sticks

you cannot use 3 sticks so
you can have all four AABB filled
The sticks in
AA do not have to match BB

So i can have
2x 1GB in AA
and
2 x 512MB in BB
or
You can put
1x 1GB in A
1x 512MB in B

but you cannot put 1GB in A and 512MB in A
it will either not boot or ignore one stick.

PS i have run an Athlon 64 with
2x DDR400 1GB in AA
2x DDR333 512 in BB
and all was recognised but ran as DDR333