How can i stack 3com 4900sx switches? Do i need accessories to do this?

take it to the 4s garage, if you want to find out the problem by yourself,you first have some professional tool , there are some diagnostic that always can figure out the problem i can show you: www.xcardiag.com/

3Com is owned by HP now.Here is the manualhttp://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c02581570/c02581570.pdf

Search the following documents for 'Password Recovery':
http://support.3com.com/infodeli/tools/switches/4500/s3n03_01_00sp01_readme.pdf
http://support.3com.com/infodeli/tools/switches/4500/3Com_Switch_4500_Command_Reference_Guide.pdf
Both of these document discuss the password recovery process for this device.

not sure about the 3COM side, but on the Cisco side... go to the configure prompt, then the port that you need to trunk (int [interface name and number] and enter)

Once you are in the interface, use the following command:
switchport trunk encap dot1q
switchport mode trunk

Then make sure that the interface is not shut down, connect the switches together and (hopefully) the 3COM will negotiate to trunking... if not you will need to manually configure the 3com.

Hope that this helps!

In order to connect a switch to a switch, unless it is auto sensing you would need a crossover cable

TCP/IP stack repair options for use with Windows XP with SP2 & Vista.

For XP, Start, Run, CMD to open a command prompt.

For Vista, Start, Programs\Accessories and right click on Command Prompt, select "Run as Administrator" to open a command prompt.

Reset WINSOCK entries to installation defaults: netsh winsock reset catalog

Reset TCP/IP stack to installation defaults. netsh int ip reset reset.log

Reboot the machine.

The primary connection method for those switches would be serial connection. In the box there should have been a DB9 serial to RJ45 cable. Hyperterminal default settings would allow you to connect.

switch dont restart by themselves without command, first remove the switch from the network, disconnect from internet, make sure you hadn't fired anybody recently it sounds like a hack. reduce network traffic to local area only and priortise important internet traffic. now got back to the switch and troubleshoot make to check the reboot command on error or when error is found, if the problem stops when the switch is remove somebody is messing with the network.or the darn switch is faulty install a new one.

Found this on 3Com website: The SuperStack 3 Switch 3870 family (3870-24 and 3870-48) can stack up to 8 units high. Stacks can be formed with any combination of 24-port and 48-port units, with a maximum of 384 (8 x 48) front panel ports supported. When connected together, a stack of units is managed as a single entity. All units in the stack need to run the same release of the operational version code (firmware). When units are stacked together, they operate in a master-slave relationship. One unit acts as a Master and the other units act as slaves. When looking at a stack of units, the master can be identified by looking at the Stack Master LED on the left side of the switch. The Stack Master LED is green for the Master. If the unit numbers are out of sync, go to the CLI command that allows users to re-number their units- system / control / renumber. This will re-number the units in the stack. It will take about a minute or two. The master is the only unit that has a visible command line interface (CLI) when a console cable is connected to it. If you connect the console cable to a slave unit, you will not see the CLI menu, but instead see slave status messages being displayed. The Master unit may not be unit 1. http://knowledgebase.3com.com/consumer/esupport.asp?id=GUIDbfa9caa4%5F138f%5F4681%5Fbaaf%5F5c99ec5b7ff4&resource=&number=0&isExternal=0&nShowFacts=&nShowCause=&nShowChange=&nShowAddInfo=&activepage=statement.asp&bForceMatch=True&strCurrentSymptom=3C17462&searchtype=normal&searchclass=&bnewsession=false&selecttype=match