Someone sat on it flat and bent rim

unbolt wheel and using tire spoons or the handle of flat ware [as long as its strong enough to not bend ]place inbetween the tire bead and rim and pry up and over rim now either use another to pry again next to spoon or slide spoon under and slide around rim removing tire reach in and remove tube check inner tire for debris fix or replace tube install
How to change and fix flat bike tire Trek Bicycle How to Fix Flat Bike Tire

You need to remove and refit wheel as it sounds as if it has not reseated properly.if it has been fitted correctly and all nuts tightened then any further wobble is either due to wheel balance ,,,, or due to compromised structure supporting wheel which need to be checked immediately..i.e. Drive shaft ....axle.....wheel bearing etc.

Do you have a bent axle. This would do that. What about a bent rim as well.

Most likely the break pad is rubbing intermittently as it rolls because the rim is bent. If its a OEM spoke rim then it wont take many curb jumps to bendit. Most mountain bikes from a walmart or academy wont be anything more than the basic for streets. If you are going off road on real mountain biking trails then you would be better off getting a stronger rim but these can be pricey. Another cause can be that the tensioner springs near the break pads need to be adjusted so you can pull the pad away from the rim. Problem is that it will take some of the stopping power away. Not recommended. Most high end mountain bikes have an actual rotor type disc break like a motor cycle that's on the inner rim so that way even if the rim gets a little bent or wet, the performance of the breaks is still up to par. To check if your rims bent, turn the bike upside down and set it so you can spin the back wheel really fast with the pedals. Then look at the tired from directly behind it. If its bent, you will see the wobble.

try wheel bearins or head stock bearings and ensure tyre is at correct psi

Call Dynacraft (bike maker) at 1-800-551-0032. My daughter's rear tire was flat and they sent out a new tube for free. She had the bike for only about 4 months. They also sent out a new rear tire as bearing/coaster brake assembly was make noises. The only problem is her original rim was purple and they sent out a silver colored rim as they don't have purple replacement part. I also had to install the tube and tire on the new rim. They only send replacement parts not assemblies.

I have a 98 heritage springer. Took it to the dealer and said the front end shakes. Without looking at it, the shop manager asked how many miles I had. Just under 10k was the answer. He said "neck bearings, it's a known issue with springer front ends that the neck bearings go after 10k miles." Taking his word for it, I agreed to have the work done. Got the bike back, no change. He said, well it needs a new front tire then. Changed the tire, again, no change. Took it to another dealer. Explained my tale of woe and the manager actually got on it and rode it. Agreeing there was something wrong, they took it in, jacked it up and actually looked at it. Turned out the rim was bent. So after all the BS at the first shop, it turns out they replaced the neck bearings and installed a new front tire on A BENT RIM! Start with the simple stuff first. Check the front wheel balance and rim straightness before diving into bearings.

700c tyres are bigger than 26".The tubes you need measure 700x28 (to32).This size is used in Hybrid style bikes.Make sure you get the same type of valve(Schreader are the same as car,Presta are narrower)or it won't fit the hole in your rim.
Make sure when inflating that the tube isn't trapped between the tyre and the rim.Only inflate to the pressure written on the sidewall of the tyre.

Hi,
A skakey front end can usually be attributed to one of four issues. Wheel bearings, warped rotor(s), bent rim, or bad tire.
To check for bearing wear, put the bike on it's center stand, or a bike jack, and have someone hold the handle bars while you try to move the wheel side to side. If you can feel excess movement, replace the wheel bearings.
Next spin the wheel and watch the rim, tire, and rotors for uneven rotation or wobbling.
Hope this helps

Tubed tire, right? COULD be a flat spot but my gut tells me the tire isn't mounted correctly. My guess is that if you look at the sidewall of the tire next to the rim on one side or the other, you'll notice that the rubber edge that sits just outside the rim isn't consistent around the entire rim because they didn't seat the bead properly. Typically all you have to do is let some air out and resituate the tire on the rim a little and keep an eye on it as you inflate it. You can overinflate the tire to around 50 to 60 PSI to help it seat correctly on the rim but be sure to reduce the air pressure--you don't want to leave it like that. The other thing it could be if it's doing this at high speeds only is that the wheel is severely out of balance, in which case you would need to take the wheel off the bike and balance it, but my gut still says it's the way the tire was installed on the bike. For those of you looking for the procedure for changing a tire and/or balancing a wheel, this is a pretty good step-by-step guide: http://www.clarity.net/~adam/tire-changing-doc.html