What Brand computer is it ?? How did you pay for the purchase ?? Have you tried calling the manufacturers support line ?? -- (they should be able to talk you through getting access and removing\changing the password or refer you to a local repair shop that does warranty repairs for their brand)
First thing I'd do is take it back and get it exchanged for a new one -- just tell them it is not working and either have them get it working or tell them to exchange it or give you a refund. (remain polite but firm and continue to ask for their boss until someone does something to fix the problem or the manager of the store tells you he can not do anything - (get names of each person you talk to and write them down) If they still will not return it - call their corporate office and file a complaint giving all names and explaining the problem. If you paid with a credit card also call the credit card company and file a dispute on the charge explaining to them that the product is not working and the store refuses to correct the problem so you want the charge reversed.
At that point call the manufacturer and their support staff should be able to get it working (either by telling you how to clear the password or by having you run a restore installation by using the disk that was included or using the hidden repair partition) If they can not get it working request that they contact the store and authorize a return or have them give you an RMA or get them to authorize a local repair shop to take it to for warranty repair (since it is under warranty it should not cost you anything and they should pay the postage if using an RMA).
Meanwhile continue to persue the complaint with Walmart and if they contact you insist that they do something to compensate you for the hassle you have had to go through to get the product working until they do something that you feel is satisfactory. If they stall in resolving the issue file a complaint with the BBB and keep in contact with your CC company to dispute the charge.
Also according to their RETURN POLICY :
Computers, camcorders, digital cameras, digital music players, e-tablets, e-readers, portable video players, GPS units, video game hardware, pre-paid cell phones, and post-paid cell phones must be returned within 15 days with a receipt.
SO if it has been less than 15 days just take it back for a refund no explanations needed !!