What can I do about a bad employment contract?

If there is currently a contract in place (a written one for a defined periods of time, which has not yet expired), your employer is still bound to it for its remaining duration: you are entitled to whatever pay, hours, duties, etc. are in that contract for its remaining length and could sue for those things (for "breach of contract") if denied them. Your employer also cannot make you sign a new contract against your will while there currently an in-effect one.
If there is presently no contract in effect, they can require you to sign a new one and terminate you if you won't. They can't hold you to its terms unless you sign. If you do sign, while it's possible, even likely, that certain of the terms you describe would not be enforced 100% as written (for example, non-competition terms are generally narrowly enforced, in terms of length, geographic reach, and type of companies/business, to do no more than is necessary to protect the former employer from competition by its former employee), 1) you can't count on that--judges sometimes do strange things or make mistakes, so a too-broad or otherwise seemingly illegal provision could be enforced if the employer sues you on it and it ends up before a judge who, rightly or wrongly, thinks it is ok; and 2) even if a judge does not enforce certain provisions fully as written, he/she may still enforce them to a degree, and that degree may be detrimental to you. If you don't want to sign the contract--and it sounds like one you should not sign--refuse to sign it and take your chances on being let go; or else talk to the employer and try to negotiate better terms (you can't force them to give you better terms). As a general rule, no matter the context, only sign contracts with whose terms you are comfortable.