Power Problem?

Last year I ran my computer off a power inverter and powered my XM reciever from the cigarette outlet. Everything worked fine. Now this year, I got a new laptop and I can't get XM to work when I have power going to my computer in the car. The people at XM sent me an AC power cord for my reciever so that I could plug it into the power inverter. Everything works fine when I use XM in my house, but when I tried to use it in the car I get a COM 4 error(COM ports are matched up though) or when I start it up it won't recognize the radio serial number even when I use the AC cord. If I don't run power to my computer and only plug the reciever into the inverter, everything works fine. I went and bought a second power inverter (300 watts) and figured that running the reciever and the computer on seperate power inverters would solve the problem. It didn't though. I don't know if my new computer is just a power hog or what. I remember reading a thread a while back about getting more power from your alternater(spelling?), but I can't find it now. I tried it in my dad's truck and had the same problem. Shouldn't my car be able to power a computer and my reciever? I would think that it has to be a power supply problem. Any advice on how to fix the problem would be greatly appreciated.
Whats the watts on the laptop and the XM receiver? Are you sure it's a continuous 300 watt inverter, rather than just a 300 watt "peak"? Also, you may need to directly wire it to your car battery, many "good" inverters include a kit so you can do this.
The laptop is DC15 volts and the reviever is DC9 volts. The power inverter is 300 watts continous. If both are running off of seperate inverters though, I would think that should provide sufficient power, assuming my car can provide enough power. I have a DC outlet in my car that runs directly from my battery that I plug one of the inverters into. The second is plugged into the cigarette outlet. The 300 watt inverter I just bought did come with the cords to hook straight onto the battery. I haven't tried plugging one into the DC outlet that already runs directly from my battery and running the other inverter directly to the battery with the cords it came with. Shouldn't the car be able to power both at the same time?
Yep, I would try direct wiring it before anything else Mike G.

I had a 200 watt inverter that barely kept my laptop alive, and that was the only thing that was connected. Now I have a power hungry widescreen laptop, which was simply too much for the inverter, so I had to upgrade. The only thing I will run from the inverter via the cig. lighter is the laptop, anything more, and a direct connection to the battery is needed.
DC wiring 101

Its not too difficult, run one red heavy gauge wire from the battery, my Astro has a tap from the under-the-hood fuse panel, I hooked in there. Then back where the inverter is to be connected, tap a ground there, I drilled a self tapper through the floorpan inside behind the panels out of sight, I know you guys are running everything near the passenger seat, mine is set up different for my aerial photography business, but that saves having to run two wires to the battery directly. Also, make sure when you route the wire under the vehicle, run it carefully and use zip ties and secure it, do not let get near anything HOT, exhaust manifold, exhaust pipe, I even routed mine around the rear AC lines just to make sure! Fuses save your equipment, I put one right as it comes out of the fuse panel, I can disconnect there if I need to do any work on the cabling. Also, one last thing, where your wire comes into the passenger compartment, use a grommet to cushion it from vibration ect. and keep moisture/bugs out.

Hope this helps!
Thanks for all the help. I am going to try to get it all setup tomorrow and see if it solves the problem. Hopefully it will so I can be out in full force on Sunday.