So my 98 Century won't start. I put the key in and I hear the beeps. I turn it to accessory and I still have power. When I turn the key to start, I hear a click or two and lose all power. Can't use anything electrical in the car. Sometimes after I attempt to start it and turn the key to off there is power, but sometimes there is not. When I checked for a short under the hood I touched the positive terminal of the battery and the horn sounded shortly. Battery voltage is 12.7. Any advice would be appreciated.

What does the voltage drop to while attempting a start?
A battery load test will tell you if there is sufficient cranking power, could be weak battery.
How old is the battery?
Is there any corrosion & terminals/ are they tight?
Have you tried a jump-start by chance?

I agree.....check voltage across the battery while attempting to crank the vehicle.......must be above 9.6 volts....

I have tried jumping the car. When I did the car had no juice. Not even the beeping sound when I put the key in the ignition. When I disconnected the jumper cables I do have juice but the symptoms are the same as I described before. I'm thinking it'* a security issue but the security light turns off when the ignition is in the run position.

Remove the neg bat cable first, then the positive.....clean any corrosion on cables, if bolts corroded replace.....install pos first, then neg.......then get a voltmeter and check voltage across battery while cranking like we asked...

I agree with Tech II. With a badly corroded or loose connection on the battery terminals, even the minor action of clipping on a jumper cable could move it enough to lose contact. The other alternative I imagine based on your description is that the engine is hydrolocked. That is much worse and much more involved than diagnosing the battery and its connections.

Did a load test last night...read 9.0. It was the battery. Put another charged battery in and it started right up. I feel like an idiot, but thank you for your help regardless.

No worries..Glad it now starts with another charged up battery.
I have one of these inexpensive 100 amp load testers, can be found online for around $35.
I remove the battery'* + & - cables then attach the tester & load it for 10 seconds.
With the 100 amp draw, it quickly gives a voltage indication & how strong or weak the battery is.

Often trickle charging overnight can restore the Cranking amps.
It is also good to check the electrolyte levels if you have removable caps, & add distilled water only if needed.

Thank you for the extra info. I am maintenance charging it now at 3 amps. I charged it at 15 amps earlier and it fully charged.

Thanks for letting us know!