DHCP Intermittent Problem

We have a 2000 server with about 50 Windows 98 clients and a mixture of 10 and 10/100 network cards. This is in a school environment. New cabling CAT6 has been installed and we have installed new 3Com 5500 switches x 2. These use fibre optic links to other parts of the building not relating to this issue.
The switches are in the same room as the machines along with the server. What happens sometimes is that the clients do not get an IP from the server. When we run a winipcfg and click renew the address pops in. On one occasion it would not get an ip so I disconneted the cable from the switch for that machine and plugged it back in and it worked. This problem varies on 10 and 10/100 cards so I don't think the issue is there. The machines are a few years old but run well and are clean as a whistle.
dbsltdAsked:
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dbsltdAuthor Commented:
Installed Unnofficial Windows 98 Service Pack and it recitifed the issue.
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blcarter14Commented:
It could be an autonegation issue.  Have you tried forcing the ports to use 100 full by any chance?  I have had issues with Winsock years ago on Win98, the following tool was useful to me.

http://www.bu.edu/pcsc/internetaccess/winsock2fix.html
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lrmooreCommented:
Do the 3Com switches have an option like Cisco's spanning-tree portfast? It could be that spanning tree hold time is lasting longer than the PC boot time and the PC just times out getting an IP address because the port isn't forwarding until a few seconds after the PC gives up. By the time you pull up ipconfig and renew, the switchport is already forwarding and bingo, you get an ip address.
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dbsltdAuthor Commented:
Reduced the speed of all the ports except that of the DHCP server to 10Mbs problem got worse. Spanning Tree is enabled. The settings are as follows Priority: 32768; STP Version: RSTP; Hello Time: 2 sec; Forwarding Delay: 15 sec; Max Aging Time: 20 sec
Can you tell me what, if any settings I need to change.
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blcarter14Commented:
How many available IP's do you have in your DHCP scope?  Do you think your running out of ip's.  You will need at least 50 to support the 50 workstations.
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dbsltdAuthor Commented:
One of the first items I checked :) I have ran through what I think are the most obvious problems with no joy.
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blcarter14Commented:
Did the problem start once the 5500's were put in?  Or had you seen this previously. Can you put in a hub or a different switch and see what happens?
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dbsltdAuthor Commented:
No problems up until June this year. School wa closed for Summer Holidays and the place rewired with CAT6 cabling and the new switches put in. Then these errors occured.
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dbsltdAuthor Commented:
Anyone any other solutions - disabled spanning tree and no difference made.
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lrmooreCommented:
Thanks for the update!
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