Computer will not boot up

i have an acer aspire t180 which is approx 5 years old. when i turned it on yesterday, the mouse and keyboard didn't work, so i plugged them into my laptop, and they were fine. After turning the pc off, and connecting them back to it, i turned it back on. All i got was a screen with acer on it with the option of pressing f12 for setup, and del for startup. Keyboard was not working again, so i had to turn it off at the wall. I opened it up, and checked the memory sticks, and they were locked in place, so i removed the round battery, and left it out for a couple of minutes. Put it back in, and put the side back on, and plugged it in. PC started up as usual, and all worked fine, keyboard, mouse everything. I turned it off, and left it for a couple of hours. When i went to use it later, i had the same thing as before, the pc came on, no beep, fan running, and acer welcome screen. Didn't go any further. Keyboard would not work, so i had to turn it off at the wall. Even if i try to startup with a disk, the drive comes on, and then turns off. I have no windows recovery disk, as the pc didn't come with one. Is it worth buying another round battery(similar to large watch battery), and trying that, or do yu think it is a fruitless task. Could it be that the pc has come to the end of the road, as if it has, we will have to lok at getting another on. Any help would be greatly appreciated.