IR reciever in my Magnavox 15MF400T/37 does not respond to the remote.

Possible manual - free Philips site with same model number:

http://www.p4c.philips.com/cgi-bin/cpindex.pl?ctn=15MF400T/37&mid=Link_FAQs&scy=US&slg=ENG

http://www.p4c.philips.com/cgi-bin/cpindex.pl?ctn=15MF400T/37&hlt=Link_UserManuals&mid=Link_UserManuals&scy=US&slg=ENG

Which brand remote control did you bought. It might haven't any setup codes in its memory, to match with Magnavox. 017,021,022,075,081,082 087,088,089,090,101,102 143,144,145,146,147,196,197. These are the setup codes to check with Magnavox. If you wish to get more, check this llink.
http://electrohelponline.blogspot.com/

are you programming the remotes with the codes for the TV manufacturer, as most Universals have to be programmed to the manufacturers remote codes to function, or Most if not all universals have a scan for the code function, refer to the manuals did theTV originally come with a remote, I am assuming so, if it didn't the TV may not have an IR reciever for the remote to work.
If this helps, please give a fixya rating, every one helps

these are the codes associated with Radio Shack's line of remotes:

One for All Universal (Radio Shack)
0054, 0179, 0030, 0020, 0024, 0096, 0186, 0171

And I was also able to find these:

UNIVERSAL REMOTE CONTROL CODE LIST for TVs
MAGNAVOX
002 009 109 118 209 309 402 408 502 508 510 807 914 917

Here is where you can get Win XP drivers:

http://www.driverupdate.net/articles/xp_download/windows-xp-driver-downloads.php?aps=winXPtextsplit2

code for dish is 579

1160 or 1161

check the cable connecting to the System unit!, it could have loosen up!
tighten it

I just programmed my comcast remote today and the codes in the manual work fine. I was lucky, the first one as the one I needed. Good luck.
11454, 10054, 10030, 10706, 10187, 10386,10802,11198,11254,11963,11990.

try going into menu. find parental control and turn it off